CN100411497C - Optical fractionation methods and apparatus - Google Patents

Abstract

Static arrays of optical traps can be used to sort microscopic objects with exponential sensitivity to size. Such optical fractionation relies on competition between an externally applied force and the moving objects' differing affinities for optical gradient traps. In a reverse fractionation method, objects that are more strongly influenced by the traps tend to become kinetically locked in to the array and are systematically deflected back into an input flow. In a thermal ratcheting method, patterns are spaced to allow particle diffusion, thus providing the opportunity for forward or reverse movement through the patterns. Unlike other sorting techniques, optical fractionation can operate continuously and can be continuously optimized. The exponential sensitivity arises quite generally from the particle size dependence of the potential wells' apparent widths.

Description

The method and apparatus of optical fractionation

Technical field

The present invention relates generally to the embodiment of the method and system of fine particle classification.Say that more specifically what the present invention is directed to is, use holographic optical tweezer technique, to such as macro molecules, biomolecule, nanoclusters, colloidal particle, and small items such as biological cell classify.

Background technology

Optical tweezers uses optical gradient forces, make small, micro-meter scale normally, the material volume along two peacekeeping three-dimensionals is absorbed in the trap.A kind of holographic format of optical tweezers, the diffractive optical element that can use a computer and produce is set up a large amount of optical tweezers from single laser beam.These tweezers can be arranged by the version of any needs according to actual requirement.

Though more known accurate and with the improved system of high relatively confidence level, common system requires the hologram that throws separately to each individual steps of particle movement.It is time-consuming calculating a plurality of holograms, and requires quite big amount of calculation.In addition, require the computer addressable projection system of the optical tweezers of realization aforementioned calculation machine generation, or other dynamics optical tweezers system, such as the scanning optical tweezers, it seems it will will be unacceptablely expensive.

Summary of the invention

The running of many technical and commercial important system is that the classical transport of the pattern by modulation potential energy produces.Utilizing a kind of method of these runnings, is optical fractionation.Optical fractionation can be small items overall, according to they different abilities by optical trap array, (in the preset time section) is categorized into composition separately continuously.Specifically, by external force, for example the object of the driving of the viscosity resistance in the working fluid runs into the optical trap array that its symmetry axis is orientated with respect to actuating force at a certain angle.In general, these traps can produce with holographic optical tweezer technique.The object that those stronger potential energy well that set up by these traps influence is tending towards jumping to a trap from a trap, thereby departs from the direction of actuating force.Stronger other objects that influenced by actuating force or not influenced by ligh trap are then by array and deviation not.Relevant with the structural form of trap, can utilize the present invention, make the different amount of heterogeneity deviation.In some cases, preferably use the clean separation of above-mentioned two composition embodiment.But, select multiple composition so that collect, be also included within the scope of the present invention.For example, in one embodiment, in the direction scope of the continuous distribution of " optics chromatography " method, can export sample heterogeneous fanwise.Can collect dividually deviation and the composition of deviation not.

In general, the composition of input sample heterogeneous and output is dispersed in the liquid by channel flow.In a preferred embodiment, passage is got the form that so-called H shape is intersected, two outputs wherein, a mixing sample that comprises input, and another only comprises background liquid, before being divided into two output channels, is brought to the distance of one section setting of flow side by side together.If passage is enough little, then the Reynold number of working fluid is also enough little, and these two kinds of fluids can not mixed, but flows abreast with layer flow mode.As a result, owing to the diffusion, the object in the input fluid can not crossed the line of demarcation between the fluid usually, enters buffer channel except that occasionally.

One aspect of the present invention relates to the optical fractionation that uses discrete optical trap array, according to small items ligh trap is reached the relative affinity that applied force is competed, and continuously small items is classified.Unwanted composition is than easier diffusion of the composition of needs or easier activity.But another aspect of the present invention relates to the optical fractionation of " on the contrary ".In opposite optical fractionation, the composition that needs is than easier diffusion of unwanted composition or easier activity.

Another aspect of the present invention relates to being called as the modification of optical peristalsis technology, in the optical peristalsis technology, and the ligh trap pattern sequence migration that small items is throwed fatefully.Difference between optical peristalsis and the disclosed optical thermal ratchet technique from giving new ability to system and method in nature, comprises hard-corely by being called the two directional pump of flux reversal effect, also possesses the new possibility that nonuniform sample is classified.

Description of drawings

Fig. 1 optical fractionation that draws, the H shape of microfluidal is wherein intersected, and comprises the first fluid that contains the nonuniform sample that will classify and by the background or second fluid that makes buffer fluid constitute;

Fig. 2 opposite optical fractionation that draws, the H shape of microfluidal is wherein intersected, and comprises two kinds of flowing liquids, a kind of nonuniform sample that will separate that comprises, another kind only comprises buffer agent solution;

The diagrammatic side view that Fig. 3 A draws optical fractionation; The draw top view of optical fractionation of Fig. 3 A of Fig. 3 B;

Fig. 4 optical fractionation of big quartz ball from little quartz ball of drawing; Fig. 4 A representative track that 0.79 micron radius ball was measured every 1/60 second that draws; Draw the simultaneously track of 0.5 micron radius ball obtaining of Fig. 4 B; Fig. 4 C is the time average surface density of 0.79 micron radius ball with respect to their centre plane density; And Fig. 4 D is the time average surface density of 0.50 micron radius ball with respect to their centre plane density;

Fig. 5 represents the spatial discrimination quality to the separation of single ligh trap line acquisition;

The draw optical peristalsis method of prior art of Fig. 6 A, wherein, a kind of ligh trap pattern makes object localization; Fig. 6 B draws with another ligh trap pattern displacement ligh trap pattern of displacement one segment distance; Fig. 6 C ligh trap pattern of another displacement that draws; At last, Fig. 6 D finishing of a circulation of optical peristalsis of drawing; With

Fig. 7 is to proving the optical thermal ratchet embodiment of flux reversal, the numerical solution of its equation of motion that draws.

Embodiment

The present invention relates to the method and apparatus of optical fractionation.An aspect relates to use the optical fractionation of discrete optical trap array, according to small items ligh trap is reached the relative affinity that applied force is competed, and continuously small items is classified.Another aspect of the present invention relates to the optical fractionation of " on the contrary ".A third aspect of the present invention relates to the use of " ratchet-type " optical fractionation technique.

For the research modulated transport, developed a kind of model system, wherein each colloidal spheres is driven, and by the regular potential well array of setting up with discrete optical tweezers, uses their motion of digital video microscopic analysis simultaneously.Experiment in this system shows that along with array rotates with respect to actuating force, driven particle is retouched out the Devil ladder system of lock-out state on the kinematics.In each of these states, the track of particle is deferred to the direction that symmetry is selected, and is irrelevant with the orientation of array by the grid of trap, thereby by lateral deflection, leaves actuating force.Can predict this deviation so that the basis of continuous isolation technics is provided, in this isolation technics, selected totally by trap array deviation, simultaneously, remaining sample passes through in the clear.This method provides the actual proof of optical fractionation, but also proof, the resolution of optical fractionation can depend on the size of particle by index law.The incomparable sensitivity of any sorting technique of report before therefore, this method provides.

People can prove the notional form of a kind of optical fractionation, prove by using discrete optical trap array, according to small items ligh trap are reached the relative affinity that applied force is competed, and can classify small items continuously.This proof utilization is dispersed in the track of two kinds of big or small colloid quartz balls of difference in the water, and these current pass through the optical tweezers linear array with the angled arrangement of current.The colloid dispersiveness that flows is limited in the glazing channel of 4mm * 0.7mm * 40 μ m, and glazing channel is bonded in side edge thereof on the microscope slide and forms.Applied pressure is poor on this passage, produces the Poisseuille stream of the constant of about 60 μ m/ seconds in several minutes.Sample comprises ball (the Duke Scientific Duke Scientific Corporation of a=0.79 μ m radius, 2463Faber Place Palo Alto, California 94303, Lot No.24169) and the ball of a=0.5 μ m radius (Duke Scientific Lot No.19057), both can use conventional bright field microscope and digital video analysis, follow the tracks of with the 30nm precision in the plane every 1/60 second.In addition, these balls can be distinguished reliably according to their outward appearance, thereby desirable model system is provided, and this model system can be monitored in real time to the microscope response of optical fractionation.The exemplary trajectory of big ball and bead is shown in Fig. 4 A and 4B respectively.

The density of quartz ball roughly is the twice of water, thereby settles into the just in time individual layer on passage lower-glass wall, and less ball is because they are lighter, and is highlyer floating.Give the Poisseuille streamline in the routing, less ball average speed is u _s=17 ± 9 μ m/ seconds are with the u of big ball _b=13 ± 2 μ m/ compare second, move slightly hurry up.The viscosity resistance F of static ball ₁=γ u is characterized by resistance coefficient γ, and resistance coefficient reaches relevant with the interfacial neighborhood of ball with the radius a of ball.Overall resistance coefficient can concern D=k by enough Einstein-Smoluchowsky _bT/ γ is from their diffusivity D estimation, K here _BT is the heat energy ratio in temperature T.And diffusivity can be measured from the track that for example is shown in Fig. 4 A and 4B in the fluctuating of lateral velocity.More generally, the power F that applies ₁Can be by providing such as processes such as electrophoretic action, electroosmosis, magnetophoresis effect or gravitational settlings.

The ligh trap that shows above is to produce with dynamic holographic optical tweezers technology.12 discrete optical tweezers, each is with the generation of 532nm laser convergence of 1.7 ± 0.8mW, be arranged in the line that becomes θ=12.0 ° ± 0.5 ° with channel axis, center to center be spaced apart b=3.6 ± 0.1 μ m.The available roughly Gauss potential well simulation of each trap, the degree of depth V of potential well _oWith width ε _T, the both is relevant with the radius a of ball.

If not to ligh trap, so by applied force F ₁When driven particle is passed through viscous liquid, will be with average speed

Move.As long as the power F that adds ₁Enough big, ligh trap makes it leave its track only a particle deviation.If deviation is little, particle will continue to move downstream so, leave the line of trap, and we can say and escape from the line of trap.On the contrary, each trap can be enough strong, and the particle deviation is advanced its contiguous influence power category.In this case, particle will be from a trap to another trap, and is caught by array effectively.The mechanism of kinematics locked-in transport that Here it is.The deflection angle θ that selects will be near the maximum deflection of this locked-in transport.The track of trapped particle is the basis with the optical fractionation classification to the relative deviation of the track of escape particle.The deviation and the composition of deviation not can be collected respectively, and Fig. 1 signal this process of drawing.

The geometry of given trap can be laser power settings between the big ball and bead escape threshold value determined by experience.The track of Fig. 4 A and 4B shows that under these conditions, bigger ball is by trap array system ground deviation, and less ball does not then have.The result is that bead flows in the shadow that produces in the big ball distribution in the clear, can collect them there.On the contrary,, concentrate in the zone that into optical trap array one end is little, can collect them there dividually by the big ball of deviation.Because concentrating of the purification of bead and big ball, be that the lateral deflection by bigger composition produces, so this optical fractionation process can continue to carry out, thereby be better than technology such as batch mode such as gel electrophoresises.

This qualitative explanation of having only few traces, the statistics by the thousands of tracks considering to collect among Fig. 4 C and the 4D more can make the people convince.At this, we with

Surface area for the center

In, describe the time average surface density n of ball , wherein overall all with average time average surface density n to each _oNormalization.Ball can be done following estimation to the relative affinity of trap: the big possibility of ball in trap than in whole fluid is big roughly 18 times, and the possibility of bead is only big 3 times.The relative velocity of given ball, these ratios so, with big ball be parked in temporarily local gesture minimum in, and slowed down simply than bead, be consistent.

The disintegrate-quality that obtains, can estimate by measuring as the relative total concentration of position function in the fluid:

$Q\left(\stackrel{\→}{r}\right)=\frac{n_b\left(\stackrel{\→}{r}\right)-n_s\left(\stackrel{\→}{r}\right)}{n_b\left(\stackrel{\→}{r}\right)+n_s\left(\stackrel{\→}{r}\right)}---\left(1\right)$

The figure of merit of following formula shown in Fig. 5 A and the 5B reaches unit of maximum, and is a unit that bears in having only the zone of bead in the zone that only comprises big ball.Crosscut represents the sample that mixes fully along one section of the fluid of Fig. 5 A line A before the trap array, and Q (y)=0 is shown in the small circle among Fig. 5 B.Behind the trap array similar one section of B along the line, drawing than great circle, there is percent 40 purification rough the displaying to big ball and bead in Fig. 5 B.Many backgrounds have contribution to the collision in the trap array, and this impact energy is escaped big ball.The escape that causes of collision is significantly in the big ball concentration curve in Fig. 4 C trap array downstream, and along with big ball saturated in trap array downstream, collision and the possibility of escaping increase gradually.Avoiding this collision most effectively, is some parallel trap lines of projection.Under this experiment condition, few can provide perfect substantially separation to three lines, in closeer suspension, need more line.

Data in Fig. 4 A, 4B and 5A, 5B show that discrete optical trap array can be continuously the size separation of napiform root according to them.Consider to cause a kind of particle to be escaped, and another kind of captive physical condition can provide the basis of optimizing optical fractionation from optical trap array.

For the sake of simplicity, analyze the influence that two discrete ligh traps are only arranged, these two ligh traps are the center with x=± b/2, and particle is near their mid point x=0.Total potential energy of particle is

$V\left(\stackrel{\→}{r}\right)=-V_0[\exp (-\frac{{(x-\frac{b}{2})}^2}{{2\mathrm{\σ}}^2})+\exp (-\frac{{(x+\frac{b}{2})}^2}{{2\mathrm{\σ}}^2})]\exp (-\frac{y^2}{{2\mathrm{\σ}}^2})-{\stackrel{\→}{F}}_1\·\stackrel{\→}{r}---\left(2\right)$

The point that particle escapes is passed through is

$=0$

Here, the y component of total power equals zero.Particle is escaped near x=0 the time probably, because the power that is absorbed in the trap is the most weak, and at y=σ, the power maximum of separation.In this case, still allow to catch the maximum obtainable deviation of track, provide by following formula

$\sin \mathrm{\θ}\≈f\left(a\right)\exp (-\frac{b^2}{8{\mathrm{\ζ}}^2})---\left(4\right)$

Here, relative trap intensity $f\left(a\right)=(2/\sqrt{e})V_o/{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C20048001339500221.png,C20048001339500241.png"\; state="\{\{state\}\}">V</figure-callout>}}_1$ With particulate material character, comprise that their size is relevant, but irrelevant with the structural form of trap.Here V ₁=F ₁σ characterizes actuating force.Similarly, the apparent expansion σ (a) of ligh trap not only depends on the width cs of focused beam _o, also depend on the size of particle:

${\mathrm{\&sigma;}}^2\left(a\right)\&ap;{\mathrm{\&sigma;}}_o^2+a^2---\left(5\right)$

Be subjected to the influence of ligh trap on wider than the smaller particle of macroparticle.This of σ to the dependence of a, separates the condition of setting up in nature for index law is sensitive.We continue to use formula (5) to illustrate.

To the V that obtains respectively at present from big ball and bead _o/ V ₁=1.3 and 0.73 data use thermal fluctuation analysis to characterize the degree of depth of ligh trap.Same the analysis showed that, the apparent widths of trap are σ=0.94 ± 0.07 μ m and 0.74 ± 0.07 μ m.These results are θ=14 ° ± 1 ° to the critical angle of big ball suggestion, and are θ=3 ° ± 2 ° to bead, and this systematically is hunted down with observed big ball and the phenomenon of bead escape is consistent.To the particle of catching reluctantly in N the trap array, total lateral deflection is (N-1) b sin θ.Therefore, by

Δ(a|b)＝bsinθ (6)

Set up the lateral deflection of each trap, thereby characterize the efficient of array.Be chosen in Δ=4/eV _o/ F ₁On trap interbody spacer b=2 σ (a) optimize this efficient.This result is useful to the design of practical optical fractionation system, but there is no need to optimize its sensitivity to particle size.

Sensitivity can be expressed as with formula

$S\left(a\right|b)\&equiv;\frac{\&PartialD;\mathrm{\&Delta;}\left(a\right|b)}{\&PartialD;a}---\left(7\right)$

And can be by following formula optimization

$\frac{\&PartialD;S\left(a\right|b)}{\&PartialD;b}=\frac{{\&PartialD;}^2\mathrm{\&Delta;}\left(a\right|b)}{\&PartialD;b\&PartialD;a}=0---\left(8\right)$

So obtain

$\frac{b^2}{2({\mathrm{\&sigma;}}_o^2+a^2)}=3-x\left(a\right)+\sqrt{9-2\mathrm{\&chi;}\left(a\right)+{\mathrm{\&chi;}}^2\left(a\right)},---\left(9\right)$

Here

$\mathrm{\&chi;}\left(a\right)=\frac{a^2+{\mathrm{\&sigma;}}_o^2}{a}\frac{f^{\&prime;}\left(a\right)}{f\left(a\right)}---\left(10\right)$

Equation (9) is set up trap interbody spacer b, by this optical trap array at interval, to captive " greatly " particle with to the differentiation of " little " particle that will escape, is the sensitiveest on angle θ.

As real example, can optimize optical fractionation in the viscous fluid with these results.To big I and optical wavelength relatively or littler particle, the degree of depth of potential well will with particle volume V _o=Aa ³Proportional, simultaneously, the radius V of viscosity resistance and particle ₁=Ba is directly proportional, so f (a) and a ²Be directly proportional.The criterion of separating based on fluid in the interval b substitution equation of optimizing (4):

$\sin \mathrm{\&theta;}\&ap;\frac{2A{a}^2}{B}\exp (\frac{{\mathrm{\&sigma;}}_o^2}{{2a}^2}-\frac{3}{4}-\frac{1}{2}\sqrt{\frac{9}{4}+\frac{{\mathrm{\&sigma;}}_o^2}{a^2}+\frac{{\mathrm{\&sigma;}}_o^4}{a^4}})---\left(11\right)$

Equation (4) and (5) show that also optical fractionation only depends on the degree of depth of potential well linearly.Therefore, the variation of the actual grade of optical vortex body actual array only makes the resolution of separation degrade linearly, and generally can be by stronger to particle size substantially dependence compensation.

In a word, previous example has in fact been used colloid quartz ball analogue system, has illustrated optical fractionation, proves that also this technology is to realizing the sensitivity of index law based on the separation of size.Aforesaid consideration illustrates, can select the geometry of optical separation system, optimize the separation based on size, and the sensitivity of index law is standard.Based on the separation of other features, can be with identical demonstration optimization, but generally can not expect to obtain the sensitivity of index law.

Equation (11) also provides understands the possibility that optical fractionation is used for protein and nanoclusters object in depth, and the yardstick a of these objects measures with tens nanometer.Specifically, equation (11) shows, on fixed angle θ, the object from the object of 1 micro-meter scale to 10 nanoscales will require ratio A/B to increase several magnitudes.This point can realize by the wavelength that the mutual effect generation resonance that increases light intensity, the wavelength that reduces it and selection and particle is strengthened on principle.

Implement optical fractionation in this system, relate to the array of setting up trap, this array is crossed over the fluid-mixing of input in a certain way, and this kind mode can make the composition of particle needs by deviation, crosses the line of demarcation, enters buffer flow.On the one hand, successful operation requires sample that enough low diffusivity or mobility are arranged, and makes unwanted composition spontaneously cross the line of demarcation with acceptable low rate.

But another aspect of the present invention is at opposite situation, and this situation is that the composition that needs is than easier diffusion of unwanted composition or easier activity.In addition, this is also more weak than another kind of composition mutual effect at the composition of needs on the one hand, thereby the situation of not selected by the optical fractionation of routine.Maximum benefit of the present invention will realize in the system that can implement two kinds of conditions, although two kinds of conditions not enough.The draw H shape of microfluidal of two kinds of liquid fluids of Fig. 1 intersects 100.A kind of fluid, promptly the input fluid 110 of Hun Heing comprises nonuniform sample to be separated.One other fluid, promptly buffer flow 120, are made of background or buffer fluid.Object in the input fluid 110 runs into the optical tweezers array 130 that becomes the θ angle to arrange with fluid, and this optical tweezers array 130 makes it to enter buffer output fluid 140 to the composition deviation of selecting in the sample, so that collect.The composition of deviation not in the sample is still stayed original liquid stream and is promptly exported in the fluid 150, is collected there.

As shown in Figure 2, replacing setting up the guiding object leaves mixing input fluid 110 and enters the optical trap array of buffer flow 120, the present invention can also when perhaps attempting to cross the line of demarcation by moving about of active, use ligh trap to guide this object to return in the fluid-mixing of input at object or by diffusion.As in conventional method shown in Figure 1, the H shape of microfluidal is intersected and 200 to be comprised two kinds of flowing liquids streams, and one of them 210 comprises nonuniform sample to be separated, and 220 of another kinds wherein comprise buffer agent solution.In the input fluid 210 that mixes, have only those to attempt to cross two kinds of marginal objects of fluid, just run into optical trap array 230, the arrangement of this optical trap array is in the input fluid 210 that is to guide object to return mixing.Cross marginal object by optical trap array 230, in buffer output fluid 240, be collected.Or those are because they are difficult for diffusion, perhaps because they by the object of optical trap array 230 deviations, are still stayed in original input fluid, can collect dividually in output fluid 250.In this case, be difficult for diffusion or more inactive object, in the input fluid that is closed by the deviation back-mixing, simultaneously more easily mobile composition will be escaped and crosses the line of demarcation and be collected from trap.Equally, the object that influenced by ligh trap more not more can be crossed the line of demarcation and is collected.

Although optical fractionation requires enough a large amount of ligh traps, to fill the input fluid of whole mixing, above-mentioned opposite process only requires enough ligh traps, to cover just in time around marginal zone between fluid.Therefore, opposite optical fractionation than the optical fractionation of routine, requires the ligh trap of much less far away, so more effectively use the laser that need set up ligh trap.

With regard to this respect, optical fractionation has proved the sorting technique that is better than other well, and opposite optical fractionation provides identical advantage.These advantages comprise: continued operation rather than batch operation; By adjusting laser power, optical maser wavelength, optical tweezers geometric configuration, actuating force and the exponential sensitivity of size being optimized continuously.Opposite optical fractionation is generalized to those conventional optical fractionations to these advantages or can not uses perhaps unpractiaca system.Because by conventional optical fractionation, opposite optical fractionation can advantageously utilize the advantage of the light polarization that forms trap, or the advantage of the beam mode structure of formation trap, according to the birefringence of object, optical activity, elasticity and such as size, light scattering cross section, absorptivity, surface charge, and character such as shape, to sorting objects.

As everyone knows, according to the diffusivity of object, to sorting objects, it is useful that the H shape of microfluidal is intersected.For opposite optical fractionation increases the optical tweezers array, greatly strengthen the selectivity of process, and provide a large amount of new physical basis object classification.

Another aspect of the present invention is to utilize thermal ratchet.Fig. 6 (A-D) principle of optical peristalsis operation institute basis of drawing, and be used to explain the characteristic of optical thermal ratchet.In Fig. 6 A, the pattern of the discrete ligh trap that draws makes the single body location.This pattern schematically is expressed as two discrete potential energy well, and width cs is respectively arranged, and the distance of separating is L.In fact, Shi Ji pattern may comprise many ligh traps that are organized into pipeline.The purpose of optical peristalsis and optical thermal ratchet method disclosed herein is that object is sent to another from a ligh trap pipeline.The difference of these two kinds of methods is how they achieve this end.

In optical peristalsis, the initial pattern of trap is replaced by another, in a back pattern, and the one section distance that can compare with σ of piping displacement (seeing Fig. 6 B).Because new potential well and old overlapping is transferred to the particle certainty pipeline nearest on the new pattern.Fig. 6 C repeats this process with the trap pattern of another displacement.When throwing original pattern, finish a circulation (see figure 6) of optical peristalsis.The net effect of this circulation is the pipeline that is absorbed in the particle trap from first pattern in the trap, is sent to the also next pipeline in first pattern.In fact, there are many particles to be absorbed in many ligh traps; And in the circulation of each optical peristalsis, all particles will be forwarded by one group of pipeline.Travel direction is definite clearly by the order of sequence, and can be by putting upside down this order conversely.

The difference of optical thermal ratchet and optical peristalsis is along the direction of motion, and the distance between the pipeline width than each trap basically is bigger.Therefore, when excitation second pattern, the particle that is absorbed in first pattern can freely spread.Those spread enough far, so that arrive the particle of nearest pipeline in second pattern, are positioned rapidly.Then, the composition that is positioned forwarded (also by diffusion) once more, and when being circulated back to first pattern, another is transmitted when projection the 3rd pattern.Different with optical peristalsis, deterministic migration in the optical peristalsis guarantees that all objects that are absorbed in the trap travel forward in each circulation, and the above-mentioned diffusion that is biased, the only certain ingredients of moving sample forward.

But the embodiment of above-mentioned thermal ratchet causes new chance.Too slow so that do not chase after the particle of the ripple of propagating forward, when the 3rd patterned illumination of Fig. 6 C, may still spread enough far, catching up with the trap of their starting points of driving in the wrong direction.These particles each the circulation in, by transmit rearward spacing between pipes from three minutes one.Pattern sequence by forming trap overall travels forward or motion backward, and be definite by the equilibrium between particle diffusion rate and the sequence cycles speed.Therefore, change the speed of circulation, can change the direction of mean motion, this phenomenon also claims flux reversal.

Under the influence of the optical tweezers pattern that circulates, can calculate the expectation flow of particle.At position x _jOn tweezers, can be with Gauss potential well simulation.

$u_j\left(x\right)=-V_o\exp (-\frac{{(x-x_j)}^2}{{2\mathrm{\&sigma;}}^2})---\left(12\right)$

This potential well has degree of depth V _oAnd width cs.This potential well obviously is the space symmetry.A state during the three-state that the pattern of trap is set up the ratchet running to be needed circulates.Example as an illustration can consider that the trap in the pattern separates with equidistance L, so the whole gesture in state k is

$V_k\left(x\right)=-\underset{i=-N}{\overset{N}{\mathrm{\&Sigma;}}}-V_o\exp (-\frac{{(x-\mathrm{jL}-k\frac{L}{3})}^2}{{2\mathrm{\&sigma;}}^2})---\left(13\right)$

Here k=0,1 or 2.Also have, as described shown in the example, the pattern of potential energy, can consider every equal time T by these three state repetitive cycling.The time that this time can spread by system with the particle of diffusivity D

$\mathrm{\&tau;}=\frac{L^2}{2D}---\left(14\right)$

Quite.The result of equilibrium between T and the τ determines that the potential energy states sequence drives the direction of particle by system.

At ligh trap with at random under the combined effect of heating power, in the dx of time t, position x, find the Brown particle Probability p (x, t) dx are determined by master equation:

p(y，t+τ)＝∫P(y，τ|x，0)p(x，t)dx (15)

Here, the propagation function to each state k is provided by following formula,

Pk(y，t|x，0)＝e ^L (16)

To time τ＜T, have:

$L\left(y\right)=D(\frac{{\&PartialD;}^2}{\&PartialD;y^2}-\mathrm{\&beta;}\frac{{\&PartialD;}^{2}V\left(y\right)}{\&PartialD;y^2})---\left(17\right)$

And β here ^-1It is the heat energy ratio.The master equation of a complete ternary circulation is,

p(y，t+3T)＝∫dy ₃P ₃(y ₃，T\y ₂，0)∫dy ₂P ₂(y ₂，T\y ₁，0)∫dy ₁P ₁(y ₁，T\x，0)p(x，t) (18)

To the optical tweezers gesture of symmetry, our consideration is that this master equation has steady state solution, can make:

p(x，t+3T)＝p(x，t) (19)

So the average speed of this stable state is provided by following formula:

$v=-\&Integral;p\left(x\right)\frac{{\&PartialD;V}_3\left(x\right)}{\&PartialD;x}+\frac{\&PartialD;p\left(x\right)}{\&PartialD;x}\mathrm{dx}---\left(20\right)$

Fig. 7 is to β V _o=10 and two typical values of σ/L, the numerical solution of this system of equations of drawing.The value very little to cycle time T, particle can not be caught up with vertiginous potential energy landscape, thus diffusion randomly; Average speed finally equals zero in this limit.If the trap in consecutive patterns overlapping (among Fig. 7 shown in σ=0.15L) passes through from a trap to a trap ground to the particle certainty, produce consistent positive drift velocity.This transmission for the cycle time T of appropriateness, reaches its maximal efficiency, and to the longer dead time, does not improve.The result is that when 1/T was in the long limit, drift velocity descended.

The trap that separates widelyer (among Fig. 7 shown in σ=0.10L) produces another kind of working order.Here, to enough big T value, particle can be caught up with the ripple of propagating forward.But, circulation faster, causing with negative v value is the flux reversal of feature.This numerical result shows such principle, utilizes this principle, can use the optical tweezers array, implements the thermal ratchet of symmetry fully with flux reversal.

As shown in Figure 7, to β V _oCertainty optical peristalsis from σ=0.15L appears in the ternary circulation of=10 Gauss trap gesture, arrives the leap of the flux reversal thermal ratchet running of σ=0.10L.

So far, the flux reversal that the variation because of cycle time T causes has been described.To different overall in the nonuniform sample, their different diffusion coefficients produce different τ values, also can cause the flux reversal effect.A kind ofly totally drive another kind totally backward forward as long as select T to drive, can cause these different totally moving in opposite directions simultaneously so.In this way, the optical thermal ratchet that has illustrated is to separating and purifying is useful by the wisp of liquid carrying.

Enforcement can reverse a kind of preferred optical approach of thermal ratchet, compares with other separation schemes based on ratchet, and be advantageous.For example, based on the thermal ratchet of arrays of interdigitated electrodes, be applied to the classification of DNA fragment.But these thermal ratchets need complicated micro production technology, and optical ratchet can be implemented at an easy rate, and can easily be assembled into the microfluidal device, for laboratory applications on the chip.Before verified, a kind of optical ratchet based on shared scanning optical tweezers of single time can cause flux reversal.Described approach depends on the asymmetric potential energy landscape in the space that is based upon on the time average meaning, thereby this system is according to the principle different with said process.In the optimum decision system of this paper explanation, each ligh trap in each pattern provides space symmetry potential energy well; And pattern self also is the space symmetry.Unidirectional migration is the sequence by at least three kinds of patterns in each circulation, utilizes the disconnection spacetime symmetry to drive.

One of symmetrical thermal ratchet example of advising previously also relates to ternary sequence.But this approach depends on the particle that only allows diffusion in a kind of state, to other two states, then plays the certainty ratchet, thereby makes the diffusion biasing.Therefore the process that illustrates in this document relates to diffusion and location in all three states, provides more selectivity and more rapidly to the classification of nonuniform sample.

Though shown and preferred embodiment be described, should be pointed out that the general personnel of this area, under the situation of the present invention that does not depart from the broad sense more, can make it and change and revise.Various characteristics of the present invention is by following claims regulation.

Claims (22)

1. one kind the equipment of the overall classification of small items, comprising:

First passage and second channel;

Drive the overall power source of small items by passage;

The a plurality of pipelines that are positioned at first passage and second channel polymerization place and are made of laser beam are so that form many ligh traps;

These ligh traps are organized into multiple pattern, and wherein, the arrangement of these patterns will make a kind of pipeline of pattern be separated by the pipeline of all the other patterns; With

These ligh traps are orientated with respect to actuating force at a certain angle, and every kind of pattern of ligh trap is arranged separately;

Wherein, the overall composition and the unwanted composition that needs that be classified as at least of small items.

2. according to the equipment of claim 1, small items wherein overall is dispersed in the liquid medium of configuration in the first passage, wherein also disposes buffer in second channel.

3. according to the equipment of claim 1, passage wherein comprises that a kind of H shape is intersected.

4. according to the equipment of claim 1, ligh trap is wherein set up by hologram optical device.

5. according to the equipment of claim 1, wherein unwanted composition is than easier diffusion of the composition of needs or easier activity.

6. according to the equipment of claim 1, wherein, the composition that needs is than easier diffusion of unwanted composition or easier activity.

7. according to the equipment of claim 1, wherein, along the distance of each pipeline enclosure of actuating force direction, greater than the width of various traps.

8. according to the equipment of claim 7, wherein, when encouraging pattern in order, ligh trap only is fit to the overall part of small items is moved forward.

9. according to the equipment of claim 7, pattern wherein is suitable for making the overall diffusion of the small items that is absorbed in the another kind of pattern when a kind of pattern of excitation.

10. overall fine particle continuously is separated into the composition that needs at least and the method for unwanted composition, comprises the steps:

A kind of overall external force that drives fine particle is provided;

The multiple pattern that respectively comprises at least one pipeline is provided, and each pipeline comprises a kind of ligh trap at least, and along the distance of each pipeline enclosure of actuating force direction, greater than the width of ligh trap;

Provide laser beam, so that form many ligh traps; With

Organize these ligh traps, make unwanted composition can leave these traps, and keep the composition that needs here.

11. according to the method for claim 10, also comprise, wherein also buffer sent in the second channel totally being dispersed in the liquid fluid of sending first passage to of fine particle.

12. according to the method for claim 10, passage wherein comprises that a kind of H shape is intersected.

13., also comprise and set up ligh trap with holographic optical tweezer technique according to the method for claim 10.

14., wherein, when encouraging pattern in order, have only the overall certain ingredients of fine particle to move forward by ligh trap according to the method for claim 10.

15. according to the method for claim 10, wherein,, be absorbed in the overall of fine particle in the another kind of pattern, can freely spread when excitation during a kind of pattern.

16. according to the method for claim 10, wherein, some particles travel forward by optical trap array, and some particles move backward by optical trap array.

17. one kind continuously the method for totally separating of fine particle, comprises the steps:

A kind of overall external force that drives fine particle is provided;

Laser beam is focused on, form many ligh traps; With

The multiple pattern that respectively comprises at least one pipeline is provided, and each pipeline comprises a kind of ligh trap at least; With

At set intervals, encourage each pattern, wherein,, be absorbed in the particle in the another kind of pattern of previous excitation, can freely spread when excitation during a kind of pattern;

Wherein, the overall composition and the unwanted composition that needs that be classified as at least of fine particle.

18., also comprise and set up ligh trap with holographic optical tweezer technique according to the method for claim 17.

19. according to the method for claim 17, wherein, along the distance of each pipeline enclosure of actuating force direction, greater than the width of various traps.

20., wherein, when encouraging pattern in order, have only the overall certain ingredients of fine particle to move forward by ligh trap according to the method for claim 17.

21. according to the method for claim 17, wherein,, be absorbed in the overall of fine particle in the another kind of pattern, can freely spread when excitation during a kind of pattern.

22. according to the method for claim 17, wherein, some particles travel forward by optical trap array, and some particles move backward by optical trap array.

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