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Deterministic bead-in-droplet ejection utilizing an integrated plug-in bead dispenser for single bead – based applications

View Article: PubMed Central - PubMed

ABSTRACT

This paper presents a deterministic bead-in-droplet ejection (BIDE) technique that regulates the precise distribution of microbeads in an ejected droplet. The deterministic BIDE was realized through the effective integration of a microfluidic single-particle handling technique with a liquid dispensing system. The integrated bead dispenser facilitates the transfer of the desired number of beads into a dispensing volume and the on-demand ejection of bead-encapsulated droplets. Single bead–encapsulated droplets were ejected every 3 s without any failure. Multiple-bead dispensing with deterministic control of the number of beads was demonstrated to emphasize the originality and quality of the proposed dispensing technique. The dispenser was mounted using a plug-socket type connection, and the dispensing process was completely automated using a programmed sequence without any microscopic observation. To demonstrate a potential application of the technique, bead-based streptavidin–biotin binding assay in an evaporating droplet was conducted using ultralow numbers of beads. The results evidenced the number of beads in the droplet crucially influences the reliability of the assay. Therefore, the proposed deterministic bead-in-droplet technology can be utilized to deliver desired beads onto a reaction site, particularly to reliably and efficiently enrich and detect target biomolecules.

No MeSH data available.


Visualization of beads in a dispensed droplet.(a) Schematic of beads aggregated during evaporation for effectively detecting and counting beads; (b) bright-field microscopy images; (c) fluorescent microscopy images of beads after evaporation. All scale bars are 50 μm.
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f5: Visualization of beads in a dispensed droplet.(a) Schematic of beads aggregated during evaporation for effectively detecting and counting beads; (b) bright-field microscopy images; (c) fluorescent microscopy images of beads after evaporation. All scale bars are 50 μm.

Mentions: To the best of our knowledge, this is the first report of a deterministic bead-in-droplet technology to accurately control the encapsulated bead number at low bead numbers (i.e., less than 10 beads) and within a fixed droplet volume. By repeatedly switching the pneumatic valve, the desired number of beads was loaded sequentially and ejected onto a cover glass. Beads in a dispensed droplet were aggregated during its evaporation, and the phenomenon facilitated the detection and counting of dispensed beads (Fig. 5a, and supplemental video clip 3). For effective bead counting and visualization, red fluorescent beads were used; a 1% (v/v) Tween 20–DI water solution was used as the buffer solution because ion crystals, which disturb bead aggregation, form during evaporation of the PBS solution. Figure 5b,c demonstrate bright-field images and fluorescent images of bead aggregates after evaporation of the dispensed droplets encapsulating a single bead to up to six beads, respectively. In case of more than 10 beads, a few beads moved toward the loading channel in the dispensing mode and not toward the nozzle. This problem can be solved through effective design of the loading site by increasing of the length (i.e., hydraulic resistance) of the loading channel and by a comprehensive analysis of streamline and bead trajectories in the dispensing mode.


Deterministic bead-in-droplet ejection utilizing an integrated plug-in bead dispenser for single bead – based applications
Visualization of beads in a dispensed droplet.(a) Schematic of beads aggregated during evaporation for effectively detecting and counting beads; (b) bright-field microscopy images; (c) fluorescent microscopy images of beads after evaporation. All scale bars are 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5385560&req=5

f5: Visualization of beads in a dispensed droplet.(a) Schematic of beads aggregated during evaporation for effectively detecting and counting beads; (b) bright-field microscopy images; (c) fluorescent microscopy images of beads after evaporation. All scale bars are 50 μm.
Mentions: To the best of our knowledge, this is the first report of a deterministic bead-in-droplet technology to accurately control the encapsulated bead number at low bead numbers (i.e., less than 10 beads) and within a fixed droplet volume. By repeatedly switching the pneumatic valve, the desired number of beads was loaded sequentially and ejected onto a cover glass. Beads in a dispensed droplet were aggregated during its evaporation, and the phenomenon facilitated the detection and counting of dispensed beads (Fig. 5a, and supplemental video clip 3). For effective bead counting and visualization, red fluorescent beads were used; a 1% (v/v) Tween 20–DI water solution was used as the buffer solution because ion crystals, which disturb bead aggregation, form during evaporation of the PBS solution. Figure 5b,c demonstrate bright-field images and fluorescent images of bead aggregates after evaporation of the dispensed droplets encapsulating a single bead to up to six beads, respectively. In case of more than 10 beads, a few beads moved toward the loading channel in the dispensing mode and not toward the nozzle. This problem can be solved through effective design of the loading site by increasing of the length (i.e., hydraulic resistance) of the loading channel and by a comprehensive analysis of streamline and bead trajectories in the dispensing mode.

View Article: PubMed Central - PubMed

ABSTRACT

This paper presents a deterministic bead-in-droplet ejection (BIDE) technique that regulates the precise distribution of microbeads in an ejected droplet. The deterministic BIDE was realized through the effective integration of a microfluidic single-particle handling technique with a liquid dispensing system. The integrated bead dispenser facilitates the transfer of the desired number of beads into a dispensing volume and the on-demand ejection of bead-encapsulated droplets. Single bead–encapsulated droplets were ejected every 3 s without any failure. Multiple-bead dispensing with deterministic control of the number of beads was demonstrated to emphasize the originality and quality of the proposed dispensing technique. The dispenser was mounted using a plug-socket type connection, and the dispensing process was completely automated using a programmed sequence without any microscopic observation. To demonstrate a potential application of the technique, bead-based streptavidin–biotin binding assay in an evaporating droplet was conducted using ultralow numbers of beads. The results evidenced the number of beads in the droplet crucially influences the reliability of the assay. Therefore, the proposed deterministic bead-in-droplet technology can be utilized to deliver desired beads onto a reaction site, particularly to reliably and efficiently enrich and detect target biomolecules.

No MeSH data available.