On-demand Milifluidic Synthesis of Quantum Dots in Digital Droplet Reactors

A do-it-yourself benchtop device for highly scalable flow synthesis of protein-based nanoparticles

Synthesis of nanoparticles is typically carried out in batch procedures, which offer limited control of parameters, and a narrow range of possible batch volumes. In contrast, flow synthesis systems, usually having a microfluidic chip as a crucial part, are devoid of these drawbacks. However, large scale devices - millifluidic systems - may offer several advantages over microfluidic systems, such as easier and cheaper production, enhanced throughput, and reduced channel clogging. Here we report a millifluidic system for the generation of protein nanoparticles, using the flow format of the original swift thermal formation technology (STF), which can process batch volume ranging from 100 µl to any practically significant amount. Capabilities of the system are demonstrated with model synthesis of Epirubicin-encapsulated BSA nanoparticles. A better degree of scalability of the synthesis over batch procedure is shown: with a 10-fold working volume increase, hydrodynamic diameter and loading capacity changed by only 10 % and 1 % respectively, compared to 60 % and 30 % for the batch synthesis. Additionally, we provide all engineering drawings, electrical circuits, programming code and nuances of assembly and operation, so that our findings can be easily reproduced. The ease of construction of the device and the superior characteristics of the resulting nanoparticles compared to the batch method indicate application potential in both the biomedical research and industrial spheres.

Spontaneous Phase Segregation Enabling Clogging Aversion in Continuous Flow Microfluidic Synthesis of Nanocrystals Supported on Reduced Graphene Oxide

Eliminating clogging in capillary tube reactors is critical but challenging for enabling continuous-flow microfluidic synthesis of nanoparticles. Creating immiscible segments in a microfluidic flow is a promising approach to maintaining a continuous flow in the microfluidic channel because the segments with low surface energy do not adsorb onto the internal wall of the microchannel. Herein we report the spontaneous self-agglomeration of reduced graphene oxide (rGO) nanosheets in polyol flow, which arises because the reduction of graphene oxide (GO) nanosheets by hot polyol changes the nanosheets from hydrophilic to hydrophobic. The agglomerated rGO nanosheets form immiscible solid segments in the polyol flow, realizing the liquid-solid segmented flow to enable clogging aversion in continuous-flow microfluidic synthesis. Simultaneous reduction of precursor species in hot polyol deposits nanocrystals uniformly dispersed on the rGO nanosheets even without surfactant. Cuprous oxide (Cu₂O) nanocubes of varying edge lengths and ultrafine metal nanoparticles of platinum (Pt) and palladium (Pd) dispersed on rGO nanosheets have been continuously synthesized using the liquid-solid segmented flow microfluidic method, shedding light on the promise of microfluidic reactors in synthesizing functional nanomaterials.

Multiplexed bio-imaging using cadmium telluride quantum dots synthesized by mathematically derived process parameters in a continuous flow active microreactor

Quantum dots (QDs) are semiconductor nanocrystals with unique size-tunable emissions. To obtain a precise emission spectrum, monodispersity in size is imperative, which is achieved by controlling the reaction kinetics in a continuous flow of active microreactors. Further, a multivariate approach (dimensional analysis) is employed to impose stringent control on the reaction process resulting in monodispersed preparation of cadmium telluride (CdTe) quantum dots. Dimensional analysis knits multiple variables into a dimensionless mathematical form which not only predicts parameters precisely to obtain narrow size tunability but also guarantees reproducibility in synthesis. Analytical, structural, and optical characterization of the microreactor synthesized polydimethylsiloxane (PDMS) coated CdTe QDs reveal quantum efficient (61.5%), photostable (44%), and biocompatible nanocrystals of 5-15 nm. Further, PDMS-coated QDs (P-QDs) are conjugated with organelle-specific antibodies/biomarkers for in-vitro imaging in NIH 3T3 cells. Likewise, proliferating cell nuclear antigen (PCNA) and anti-myosin (MF20), cardiomyocytes antibodies are conjugated with P-QDs (red and green, respectively) to image the zebrafish's cardiac tissue. Antibodies tagged with quantum dots are imaged simultaneously using confocal microscopy. Thus, multiplexed bio-imaging of in-vitro and zebrafish tissue is demonstrated successfully. The results indicate the suitability of continuous flow active microreactor in conjunction with the mathematical prediction of process parameters to synthesize reproducibly monodispersed and quantum efficient QDs.

Flexible online in-droplet cell/synthetic particle concentration utilizing alternating current electrothermal-flow field-effect transistor

Cell/particle concentration inside droplets holds great potential in extending lab-in-a-droplet applications, typically ranging from biological and chemical assays. Herein, we present a universal, massive and versatile technique, namely, alternating current electrothermal-flow field-effect transistor (ACET-FFET) to accomplish in-droplet cell/synthetic particle concentration on demand. Three parallel planar electrodes are utilized to generate an artificially reorderable electric field inside droplets by tuning the gate voltage through field-effect control, which results in a reshapable ACET-based microvortices pattern for in-droplet concentration. A downstream Y-shaped junction promotes the mother droplet splitting into two daughter droplets containing highly and poorly concentrated cells/particles, respectively. Fluorescent polystyrene (PS) nanoparticles are used to characterize the variations of ACET-microvortices flow pattern formation within droplets. Moreover, the concentration performance is demonstrated using PS microparticles and Neurospora crassa cells. We show that particles/cells can flexibly accumulate into any daughter droplet or be equally concentrated in both daughter droplets by conveniently regulating the gate voltage. The highly concentrated cells at the entrance of the concentrator show an instantaneous response performance to the external electric field. Further, online simultaneous particle synthesis and concentration inside droplets are proposed and implemented for the first time, demonstrated by efficient in-droplet micromixing and Prussian blue (PB) reaction. The accompanying synthetic PB particles are highly concentrated into either daughter droplet, thereby extending the versatility of the platform. The presented in-droplet concentration strategy, together with its unique features of simple geometric configuration, facile operation and broad applicability can broaden utility in droplet microfluidics.

Microfluidic synthesis of quantum dots and their applications in bio-sensing and bio-imaging

Bio-sensing and bio-imaging of organisms or molecules can provide key information for the study of physiological processes or the diagnosis of diseases. Quantum dots (QDs) stand out to be promising optical detectors because of their excellent optical properties such as high brightness, stability, and multiplexing ability. Diverse approaches have been developed to generate QDs, while microfluidic technology is one promising path for their industrial production. In fact, microfluidic devices provide a controllable, rapid and effective route to produce high-quality QDs, while serving as an effective in situ platform to understand the synthetic mechanism or optimize reaction parameters for QD production. In this review, the recent research progress in microfluidic synthesis and bio-detection applications of QDs is discussed. The definitions of different QDs are first introduced, and the advances in microfluidic-based fabrication of quantum dots are summarized with a focus on perovskite QDs and carbon QDs. In addition, QD-based bio-sensing and bio-imaging technologies for organisms of different scales are described in detail. Finally, perspectives for future development of microfluidic synthesis and applications of QDs are presented.