Bead trapping

It is very instructive to work out in detail the flucmations of a bead trapped in a moving potential. This case is of great interest for at least two reasons. First, it provides a simple example of both a NETS and a NESS that can be analytically solved in detail. Second, it can be experimentally realized by trapping micronsized beads using optical tweezers. The first experiments studying nonequilibrium fluctuations in a bead in a trap were carried out by Evans and collaborators [57] and later on extended in a series of works [58, 59]. Mazonka and Jarzynski [60] and later Van Zon and Cohen [61-63] have carried out... 

Figure 8. A molecular system of extension x is connected at its leftmost end to a bead trapped in an optical well (or to the tip of an AFM cantilever) and at its rightmost end to an immobilized surface (or a bead fixed to the tip of a micropipette). The position of the bead relative to the center of the trap, xt, gives a readout of the acting force / = KXi,. The control parameter in this setup is Z = Xb + X, whereas both xt and x are fluctuating quantities.

FIGURE 8.3 Different microfilter designs, (a) The filter pillars are placed inside the channel, (b) The channel is widened at the bead-trapping location, (c) The filter pillars define a square reaction chamber where the beads are collected [831], Reprinted with permission from Elsevier Science. 

In one report, the activity of the HRP enzyme was studied by CL detection using the xanthine/xanthine oxidase (XOD)/luminol system. The enzymes were immobilized on glass beads trapped in a reaction chamber by weirs. It was found that when HRP was immobilized, a greater CL signal was generated than with free-solution HRP. However, when XOD (not HRP) was immobilized, enzymatic reaction products were not detectable. This was probably because the immobilized XOD enzyme had a low specific activity [721]. 

Lettieri, G.L., Dodge, A., Boer, G., de Rooij, N.F., Verpoorte, E., A novel micro-fluidic concept for bioanalysis using freely moving beads trapped in recirculating flows. Labchip 2003, 3, 34-39. 

Figure 10 Time-lapse sequence (side-view cross section) of a sample plug, transported through the bead trap of the weir-SMEC and into the exiting flow channel. Four time points during the passage of the sample are monitored in these images. The length of each legend indicates the flow velocity.

Figure 12 Combination of dielectrophoretic field cage (DFC) and optical tweezers (OT) for the measurement of bead-cell adhesion (A) 4.1-(xm polystyrene particle trapped with laser tweezers (right) in contact with T-lymphoma cell ( — 1 5 pm in diameter). Cell and bead were brought into contact. The time for stable adhesion was measured. (B) Schematic representation of the experimental system used to measure the adhesion forces between bead and cell with the cell trapped in a DFC and the bead trapped in the laser focus of the OT. (C) Probing different surface regions of the cell for bead-cell adhesion (five beads are attached to a single cell). (Reprinted from Ref. 91 with permission.)...

Fig. 3 Scanning electron microscopy (SEM) images of (a) a 150 pm-diameter latex beads spot, (b) a closer view of the latex beads arrangement within a spot (reproduced from [13]) (with permission) (c) immobilized streptavidine-coated beads (2.8 jim) on a biotin modified surface (reproduced from [14]) (with permission), (d) 3D representation of the SEM image of a Sepharose bead trapped at the PDMS/air interface (reproduced from [15]) (with permission)...

FIG. 15.4 Light-driven motion of a gjasa bead trapped in an NPC-02 droplet. The glass bead was captured under alternating UV and blue-light photoirradiation (a, b, and c) and conve> d by the alternating photoirradiation (d and e). 

Fig. 12.2. Forward and backward step movement of kinesin. (a) A single kinesin molecule moving on microtubules. A kinesin molecule is attached to a bead trapped by a focused laser as a cargo for measurements, (b) Time trajectory of displacement and force of kinesin. In the laser trap measurement, when kinesin moves the trapping force or external load increases indicted, (c) Energy landscape for the forward and backward step of kinesin. The thermodynamic parameters obtained for the forward and backward step movement of kinesin are included in the figure. The rates for the forward and backward steps, fc , are related to the activation energy U and external load F,...

Take sufficient Dynabeads M280 precoated with secondary antibody for the number of immunoprecipitation reactions proposed in a 1.5-mL Eppendorf tube and concentrate in MPC by placing in MPC rack for 2 min, tilting rack to horizontal at 1 min to remove any beads trapped in lid. Remove supernatant with a pipet and resuspend Dynabeads in 1 mL of PBS/BSA. Repeat, washing a total of two times. 

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