A perm-selective nanochannel could initiate concentration polarization near the nanochannel, significantly decreasing (increasing) the ion concentration in the anodic (cathodic) end of the nanochannel. Such strong concentration polarization can be induced even at moderate buffer concentrations because of local ion depletion (therefore thicker local Debye layer) near the nanochannel. In addition, fast fluid vortices were generated at the anodic side of the nanochannel due to the nonequilibrium electro-osmotic flow (EOF), which was at least $\sim 10\times$ faster than predicted from any equilibrium EOF. This result corroborates the relation among induced EOF, concentration polarization, and limiting-current behavior.

In this paper, we report a new method of fabricating a high-throughput protein preconcentrator in poly(dimethylsiloxane) (PDMS) microfluidic chip format. We print a submicron thick ion-selective membrane on the glass substrate by using standard patterning techniques. By simply plasma-bonding a PDMS microfluidic device on top of the printed glass substrate, we can integrate the ion-selective membrane into the device and rapidly prototype a PDMS preconcentrator without complicated microfabrication and cumbersome integration processes. The PDMS preconcentrator shows a concentration factor as high as ∼10⁴ in 5 min. This printing method even allows fabricating a parallel array of preconcentrators to increase the concentrated sample volume, which can facilitate an integration of our microfluidic preconcentrator chip as a signal enhancing tool to various detectors such as a mass spectrometer.

We report on a novel technique of resonant frequency shift measurement based on a nanomechanical cantilever with a PZT actuating layer for label-free detection of a prostate-specific antigen (PSA) in a liquid environment. The nanomechanical PZT thin film cantilever is composed of SiO₂/Ta/Pt/PZT/Pt/SiO₂ on a SiN_x supporting layer for simultaneous self-exciting and sensing; it was fabricated using a standard MEMS (micro electromechanical system) process. The specific binding characteristics of the PSA antigen to its antibody, which is immobilized with Calixcrown self-assembled monolayers (SAMs) on a gold surface deposited on a cantilever, are determined to a high sensitivity. For the bioassay in a liquid environment, a liquid test cell with a 20 µl volume reaction chamber has been fabricated, using a bonding technique between poly(dimethyl siloxane) (PDMS) bilayers. An observed trend of resonant frequency change with respect to time could be explained by the binding kinetics due to the Langmuir isotherm and diffusion and by the effects of a small volume reaction chamber. In the saturated regimes, the resonant frequency of the cantilever increased with increase of the PSA concentration in the reaction chamber, showing that the trend of the resonance frequency change was similar to that of the fluorescence results. The saturated resonance frequency shift of the cantilever was proportional to the PSA antigen concentration of analyte solution.

Prominent techniques such as real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and rapid kits are currently being explored to both enhance sensitivity and reduce assay time for diagnostic tests. Existing commercial molecular methods typically take several hours, while immunoassays can range from several hours to tens of minutes. Rapid diagnostics are crucial in Point-of-Care Testing (POCT). We propose an approach that integrates a time-series deep learning architecture and AI-based verification, for the enhanced result analysis of lateral flow assays. This approach is applicable to both infectious diseases and non-infectious biomarkers. In blind tests using clinical samples, our method achieved diagnostic times as short as 2 minutes, exceeding the accuracy of human analysis at 15 minutes. Furthermore, our technique significantly reduces assay time to just 1-2 minutes in the POCT setting. This advancement has the potential to greatly enhance POCT diagnostics, enabling both healthcare professionals and non-experts to make rapid, accurate decisions.