Accelerated immunoassays based on magnetic particle dynamics in a rotating capillary tube with stationary magnetic field

Magnetic nanochains-based dynamic ELISA for rapid and ultrasensitive detection of acute myocardial infarction biomarkers

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality globally. The serum levels of a group of cardiac biomarkers have been regarded as important indicators in the routine diagnosis of AMI. The development of rapid, sensitive, and accurate detection methods of AMI biomarkers is urgently needed for the early diagnosis of AMI. Here, a dynamic and pseudo-homogeneous enzyme-linked immunosorbent assay (ELISA) was reported based on the combined use of bioconjugated magnetic nanochains (MNCs) and gold nanoparticles (AuNPs) probes. The capture antibodies-conjugated MNCs served as dynamic nano-mixers to facilitate liquid mixing and as homogeneously dispersed capturing agents to capture and separate specific targets. The AuNPs probes were prepared by co-immobilization of detection antibodies and horseradish peroxidase (HRP) for signals amplification. The design of bioconjugated MNCs and AuNPs probes significantly increased the assay kinetics and improves the assay sensitivity. This novel ELISA strategy realized accurate detection of a panel of AMI biomarkers within 35 min, leading to considerably improved sensitivities compared to that of conventional ELISA method.

A localized surface acoustic wave applied spatiotemporally controllable chemical gradient generator

In many research studies and applications about microscale biochemical analysis, the generation of stable, spatiotemporally controllable concentration gradients is critical and challenging. However, precise adjustment of concentration gradients in microchannels is still a huge challenge. Because of its precise controllability, non-harmfulness, and immediacy, sound waves perfectly meet the needs of this type of problem. Utilizing the acoustofluidic platform to manipulate liquids in the microchannel accurately makes it an excellent solution to this problem. In this work, we present a tunable and reliable acoustofluidic gradient generator, which can trigger a change of medium based on acoustic streaming induced by C-shaped interdigital transducers (IDTs). By locally generating streaming via two C-shaped IDTs in the same direction but at different horizontal positions, concentration generators can produce two streams of liquids step by step, forming a stable and controllable concentration gradient within short response times (approximately second response time). Along with this gradient generator's advantages in size, tunability, and reliability, it could be widely used for micro-biological and micro-chemical applications requiring a precise concentration gradient.

Rotating magnetic particles for lab-on-chip applications - a comprehensive review

Magnetic particles are widely used in lab-on-chip and biosensing applications, because they have a high surface-to-volume ratio, they can be actuated with magnetic fields and many biofunctionalization options are available. The most well-known actuation method is to apply a magnetic field gradient which generates a translational force on the particles and allows separation of the particles from a suspension. A more recently developed magnetic actuation method is to exert torque on magnetic particles by a rotating magnetic field. Rotational actuation can be achieved with a field that is uniform in space and it allows for a precise control of torque, orientation, and angular velocity of magnetic particles in lab-on-chip devices. A wide range of studies have been performed with rotating MPs, demonstrating fluid mixing, concentration determination of biological molecules in solution, and characterization of structure and function of biomolecules at the single-molecule level. In this paper we give a comprehensive review of the historical development of MP rotation studies, including configurations for field generation, physical model descriptions, and biological applications. We conclude by sketching the scientific and technological developments that can be expected in the future in the field of rotating magnetic particles for lab-on-chip applications.

Catalytic Janus Colloids: Controlling Trajectories of Chemical Microswimmers

Catalytic Janus colloids produce rapid motion in fluids by decomposing dissolved fuel. There is great potential to exploit these "autonomous chemical swimmers" in applications currently performed by diffusion limited passive colloids. Key application areas for colloids include transporting active ingredients for drug delivery, gathering analytes for medical diagnostics, and self-assembling into regular structures used for photonic materials and lithographic templating. For drug delivery and medical diagnostics, controlling colloidal motion is key in order to target therapies, and transport analytes through lab-on-a-chip devices. Here, the autonomous motion of catalytic Janus colloids can remove the current requirements to induce and control colloid motion using external fields, thereby reducing the technological complexity required for medical therapies and diagnostics. For materials applications exploiting colloidal self-assembly, the additional interactions introduced by catalytic activity and rapid motion are predicted to allow access to new reconfigurable and responsive structures. In order to realize these goals, it is vital to develop methods to control both individual colloidal paths and collective behavior in motile catalytic colloidal systems. However, catalytic Janus colloids' trajectories are randomized by Brownian effects, and so require new strategies in order to be harnessed for transport. This is achievable using a variety of different approaches. For example, self-assembly and control of catalyst geometry can introduce controlled amounts of rotary motion, or "spin" into chemical swimmer trajectories. Furthermore, rotary motion combined with gravity, produces well-defined orientated helical trajectories. In addition, when catalytic colloids interact with topographical features, such as edges and trenches, they are steered. This gives rise to a new approach for autonomous colloidal microfluidic transport that could be deployed in future lab-on-a-chip devices. Chemical gradients can also influence the motion of catalytic Janus colloids, for example, to cause collective accumulations at specific locations. However, at present, the predicted theoretical degree of control over this phenomenon has not been fully verified in experimental systems. Collective behavior control for chemical swimmers is also possible by exploiting the potential for the complex interactions in these systems to allow access to self-assembled, dynamic and reconfigurable ordered structures. Again, current experiments have not yet accessed the breadth of possible behavior. Consequently, continued efforts are required to understand and control these interaction mechanisms in real world systems. Ultimately, this will help realize the use of catalytic Janus colloids for tasks that require well-controlled motion and structural organization, enabling functions such as analyte capture and concentration, or targeted drug delivery.

Development and Comparison of Two Immuno-disaggregation Based Bioassays for Cell Secretome Analysis

Cell secretome analysis has gained increasing attention towards the development of effective strategies for disease treatment. Analysis of cell secretome enables the platform to monitor the status of disease progression, facilitating therapeutic outcomes. However, cell secretome analysis is very challenging due to its versatile and dynamic composition. Here, we report the development of two immuno-disaggregation bioassays using functionalized microparticles for the quantitative analysis of the cell secretome. Methods: We evaluated the feasibility of our developed immuno-disaggregation bioassays using antibody-conjugated MPs and protein-conjugated MPs for the detection of target cell secretome protein. The vascular endothelial growth factor (VEGF)-165 protein was tested as a model cell secretome protein in the serum and serum-free conditions. The status of MP aggregates was examined with a light microscopy and AccuSizer^TM 780 Optical Particle Sizer. The accuracy of our bioassays measurement was compared with standard ELISA method. Results: The developed bioassays successfully detected target VEGF protein present in serum-free buffer and serum-containing complete cell culture medium with high sensitivity and specificity. Additionally, the immuno-disaggregation bioassays using antibody-conjugated MPs and protein-conjugated MPs have a wide detection range from 0.01 ng/mL to 100 ng/mL and 0.5 ng/mL to 100 ng/mL, respectively. The sensitivity of the bioassay using antibody-conjugated MPs was approximately one order of magnitude higher than the bioassay using protein-conjugated MPs. Conclusion: Our promising results indicate the potential of the developed bioassays as powerful platforms for the quantitative analysis of cell secretome.

Integrated lab-on-chip biosensing systems based on magnetic particle actuation--a comprehensive review

The demand for easy to use and cost effective medical technologies inspires scientists to develop innovative lab-on-chip technologies for point-of-care in vitro diagnostic testing. To fulfill medical needs, the tests should be rapid, sensitive, quantitative, and miniaturizable, and need to integrate all steps from sample-in to result-out. Here, we review the use of magnetic particles actuated by magnetic fields to perform the different process steps that are required for integrated lab-on-chip diagnostic assays. We discuss the use of magnetic particles to mix fluids, to capture specific analytes, to concentrate analytes, to transfer analytes from one solution to another, to label analytes, to perform stringency and washing steps, and to probe biophysical properties of the analytes, distinguishing methodologies with fluid flow and without fluid flow (stationary microfluidics). Our review focuses on efforts to combine and integrate different magnetically actuated assay steps, with the vision that it will become possible in the future to realize integrated lab-on-chip biosensing assays in which all assay process steps are controlled and optimized by magnetic forces.

Accelerated surface-enhanced Raman spectroscopy (SERS)-based immunoassay on a gold-plated membrane

A rapid and simple SERS-based immunoassay has been developed to overcome diffusion-limited binding kinetics that often impedes rapid analysis in conventional heterogeneous immunoassays. This paper describes the development of an antibody-modified membrane as a flow-through capture substrate for a nanoparticle-enabled SERS immunoassay to enhance antibody-antigen binding kinetics. A thin layer of gold is plated onto polycarbonate track-etched nanoporous membranes via electroless deposition. Capture antibody is immobilized onto the surface of a gold-plated membrane via thiolate coupling chemistry to serve as a capture substrate. A syringe is then used to actively transport the analyte and extrinsic Raman labels to the capture substrate. The fabrication of the gold-plated membrane is thoroughly investigated and established as a viable capture substrate for a SERS-based immunoassay in the absence of sample/SERS label flow. A syringe pump is used to systematically investigate the effect of flow rate on antibody-antigen binding kinetics and demonstrate that active transport to the capture membrane surface expedites antibody-antigen binding. Mouse IgG and goat anti-mouse IgG are selected as a model antigen-antibody system to establish proof of principle. It is demonstrated that the assay for mouse IgG is reduced from 24 h to 10 min and a 10-fold improvement in detection limit is achieved with the flow assay developed herein relative to the passive, i.e., no flow, assay. Moreover, mouse serum is directly analyzed and IgG level is determined using the flow assay.

A portable flow-through fluorescent immunoassay lab-on-a-chip device using ZnO nanorod-decorated glass capillaries

We report a portable flow-through fluorescent immunoassay lab-on-a-chip device using inexpensive disposable glass capillaries for medical diagnostics. The device is made up of a number of serially connected glass capillaries, of which each interior surface is grown using zinc oxide (ZnO) nanorods, which different probe antibodies are attached to. The ZnO nanorods not only provide a large surface area for high density probe attachment, but also enhance the fluorescent signals to significantly improve the detection signal responses. The glass capillary also allows for convenient flow-through detection. Coupled with a homemade handheld analyzer integrated with an automatic pump system and a fluorescence readout module, a portable immunoassay capillary device enables quantitative detection of multiple biomarkers in 30 min with detection limits of 1-5 ng mL(-1) and wide dynamic ranges for prostate specific antigen (PSA), α-Fetoprotein (AFP) and carcinoembryonic antigen (CEA) in serum. This new conceptual lab-on-a-chip device eliminates the need for expensive micro-fabrication processes, while offering inexpensive and disposable, but replaceable tube-type "microchannels" for multiplexed detection in portable clinical diagnostics.