As a typical, classical, but powerful biochemical sensing technology in analytical chemistry, enzyme-linked immunosorbent assay (ELISA) shows excellence and wide practicability for quantifying analytes of ultralow concentration. However, long incubation time and burdensome laborious multistep washing processes make it inefficient and labor-intensive for conventional ELISA. Here, we propose rod-like magnetically driven nanorobots (MNRs) for use as maneuverable immunoassay probes that facilitate a strategy for an automated and highly efficient ELISA analysis, termed nanorobots enabled ELISA (nR-ELISA). To prepare the MNRs, the self-assembled chains of Fe3O4 magnetic particles are chemically coated with a thin layer of rigid silica oxide (SiO2), onto which capture antibody (Ab1) is grafted to further achieve magnetically maneuverable immunoassay probes (MNR-Ab1s). We investigate the fluid velocity distribution around the MNRs at microscale using numerical simulation and empirically identify the mixing efficiency of the actively rotating MNRs. To automate the analysis process, we design and fabricate by 3-D printing a detection unit consisting of three function wells. The MNR-Ab1s can be steered into different function wells for required reaction or wishing process. The actively rotating MNR-Ab1s can enhance the binding efficacy with target analytes at microscale and greatly decrease incubation time. The integrated nR-ELISA system can significantly reduce the assay time, more importantly during which process manpower input is greatly minimized. Our simulation of the magnetic field distribution generated by Helmholtz coils demonstrates that our approach can be scaled up, which proves the feasibility of using current strategy to construct high throughput nR-ELISA detection instrument. This work of taking magnetic micro/nanobots as active immunoassay probes for automatic and efficient ELISA not only holds great potential for point-of-care testing (POCT) in future but also extends the practical applications of self-propelled micro/nanorobots into the field of analytical chemistry.

Biosensing using liquid crystals has a tremendous potential by coupling the high degree of sensitivity of their alignment to their surroundings with clear optical feedback. Many existing setups use birefringence of nematic liquid crystals, which severely limits straightforward and frugal implementation into a sensing platform due to the sophisticated optical set-ups required. In this work, we instead utilize chiral nematic liquid crystal microdroplets, which show strongly reflected structural color, as sensing platforms for surface active agents. We systematically quantify the optical response of closely related biological amphiphiles and find unique optical signatures for each species. We detect signatures across a wide range of concentrations (from micromolar to millimolar), with fast response times (from seconds to minutes). The striking optical response is a function of the adsorption of surfactants in a nonhomogeneous manner and the topology of the chiral nematic liquid crystal orientation at the interface requiring a scattering, multidomain structure. We show that the surface interactions, in particular, the surface packing density, to be a function of both headgroup and tail and thus unique to each surfactant species. We show lab-ona-chip capability of our method by drying droplets in high-density two-dimensional arrays and simply hydrating the chip to detect dissolved analytes. Finally, we show proof-of-principle in vivo biosensing in the healthy as well as inflamed intestinal tracts of live zebrafish larvae, demonstrating CLC droplets show a clear optical response specifically when exposed to the gut environment rich in amphiphiles. Our unique approach shows clear potential in developing on-site detection platforms and detecting biological amphiphiles in living organisms.

Generating and maintaining the concentration dilutions of diffusible molecules in microchannels is critical for high-throughput chemical and biological analysis. Conventional serial network microfluidic technologies can generate high orders of arbitrary concentrations by a predefined microchannel network. However, a previous design requires a large occupancy area and is unable to dynamically generate different profiles in the same chip, limiting its applications. This study developed a microfluidic device enabling dynamic variations of both the concentration in the same channel and the concentration distribution in multiple channels by adjusting the flow resistance using programmable pneumatic microvalves. The key component (the pneumatic microvalve) allowed dynamic adjustment of the concentration profile but occupied a tiny space. Additionally, a Matlab program was developed to calculate the flow rates and flow resistance of various sections of the device, which provided theoretical guidance for dimension design. In silico investigations were conducted to evaluate the microvalve deformation with widths from 100 to 300 µm and membrane thicknesses of 20 and 30 µm under the activation pressures between 0 and 2000 mbar. The flow resistance of the deformed valve was studied both numerically and experimentally and an empirical model for valve flow resistance with the form of Rh=aebP was proposed. Afterward, the fluid flow in the valve region was characterized using Micro PIV to further demonstrate the adjustment mechanism of the flow resistance. Then, the herringbone structures were employed for fast mixing to allow both quick variation of concentration and minor space usage of the channel network. Finally, an empirical formula-supported computational program was developed to provide the activation pressures required for the specific concentration profile. Both linear (Ck = −0.2k + 1) and nonlinear (Ck = (110)k) concentration distribution in four channels were varied using the same device by adjusting microvalves. The device demonstrated the capability to control the concentration profile dynamically in a small space, offering superior application potentials in analytical chemistry, drug screening, and cell biology research.

Biosensing using liquid crystals has a tremendous potential by coupling the high degree of sensitivity of their alignment to their surroundings with clear optical feedback. Many existing set-ups use birefringence of nematic liquid crystals, which severely limits straightforward and frugal implementation into a sensing platform due to the sophisticated optical set-ups required. In this work, we instead utilize chiral nematic liquid crystal micro-droplets, which show strongly reflected structural colour, as sensing platforms for surface active agents. We systematically quantify the optical response of closely related biological amphiphiles and find unique optical signatures for each species. We detect signatures across a wide range of concentrations (from μM to mM), with fast response times (from seconds to minutes). The striking optical response is a function of the adsorption of surfactants in a non-homogeneous manner and the topology of the liquid crystal orientation at the interface requiring a scattering, multidomain structure, which we observe to be different between molecules. We show lab-on-a-chip capability of our method by drying droplets in high-density two-dimensional arrays and simply hydrating the chip to detect dissolved analytes. Finally, we show proof-of-principle in vivo biosensing in the intestinal tracts of live zebrafish larvae, demonstrating CLC droplets show a clear and differential optical response between healthy and inflamed tissues. Our unique approach has great potential in developing on-site detection platforms and detecting biological amphiphiles in living organisms.