Anyang Wang

Photoelectrochemical (PEC) sensors integrate light excitation with electrochemical detection, providing low background noise and robust anti-interference capabilities. Surface plasmon resonance (SPR) acts as an effective light antenna for signal transduction in these sensors. Traditionally, plasmon-mediated PEC sensors operate via hot carrier injection, which necessitates direct contact between the plasmonic antenna and the semiconductor, thereby limiting sensor design flexibility. In this work, we introduce plasmon-induced resonance energy transfer (PIRET) as a novel signal transduction mechanism in a PEC immunosensor. A Bi ₃ FeMo ₂ O ₁₂ (BFMO) semiconductor thin film is functionalized with capture antibodies, while plasmonic Au nanoparticles with absorption spectrum overlapping with BFMO are conjugated to detection antibodies. Upon target antigen binding, the Au nanoparticles are positioned in proximity to the BFMO surface through a sandwich immunoassay configuration, enabling PIRET-mediated generation of electron-hole pairs in BFMO. Using human IgG as a model analyte, we demonstrate the feasibility and advantages of PIRET, highlighting its potential to extend PEC sensor design by permitting a physical gap between the plasmonic antenna and semiconductor.

A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called “pysanky” a series of microfluidic devices were created. Pysanky is the use of a heated wax stylus, known as a “kistka”, to create micro-sized, intricate designs on the surface of an egg. The proposed technique involves the modification of an x-y-z actuation translation system with a wax extruder tip in junction with Polydimethysiloxane (PDMS) device fabrication techniques. Initial system optimization was performed considering design parameters such as extruder tip size, contact angle, write speed, substrate temperature, and wax temperature. Channels created ranged from 160 to 900 μm wide and 10 to 150 μm high based upon system operating parameters set by the user. To prove the capabilities of this technology, a series of microfluidic mixers were created via the wax technique as well as through traditional photolithography: a spiral mixer, a rainbow mixer, and a linear serial dilutor. A thermo-fluidic computational fluid dynamic (CFD) model was generated as a means of enabling rational tuning, critical to the optimization of systems in both normal and extreme conditions. A comparison between the computational and experimental models yielded a wax height of 57.98 μm and 57.30 μm, respectively, and cross-sectional areas of 11,568 μm² and 12,951 μm², respectively, resulting in an error of 1.18% between the heights and 10.76% between the cross-sectional areas. The device’s performance was then compared using both qualitative and quantitative measures, considering factors such as device performance, channel uniformity, repeatability, and resolution.

Suitable micropumping methods for flow control represent a major technical hurdle in the development of microfluidic systems for point-of-care testing (POCT). Passive micropumping for point-of-care microfluidic systems provides a promising solution to such challenges, in particular, passive micropumping based on capillary force and air transfer based on the air solubility and air permeability of specific materials. There have been numerous developments and applications of micropumping techniques that are relevant to the use in POCT. Compared with active pumping methods such as syringe pumps or pressure pumps, where the flow rate can be well-tuned independent of the design of the microfluidic devices or the property of the liquids, most passive micropumping methods still suffer flow-control problems. For example, the flow rate may be set once the device has been made, and the properties of liquids may affect the flow rate. However, the advantages of passive micropumping, which include simplicity, ease of use, and low cost, make it the best choice for POCT. Here, we present a systematic review of different types of passive micropumping that are suitable for POCT, alongside existing applications based on passive micropumping. Future trends in passive micropumping are also discussed.

Polydimethylsiloxane (PDMS) is a flexible and biocompatible material widely used in the fabrication of microfluidic devices, and is often studied for the fabrication of flexible electrodes. The most popular method of fabricating a flexible electrode using PDMS is done by transferring a metal electrode onto said PDMS. However, the transfer process is difficult and the transferred metal layer is easily damaged due to inherently weak adhesion forces between the metal and PDMS, thus requiring a chemical treatment or sacrificial layer between the two. The fabrication process using a chemical treatment or sacrificial layer is complicated and expensive, which is the major limitation of using PDMS in the fabrication of flexible electrodes. This paper discusses the findings of a possible solution to create strong bonding between PDMS and various metals (copper, nickel and silver) using a chemical-free metal to PDMS thermal bonding technique. This method is the same as the PDMS curing process, but with a variation in the curing condition. The condition required to create strong bonding was studied by observing copper transferred by various PDMS curing conditions, including the standard condition. The condition creating the strong bonding was baking PDMS (5:1 = base polymer: curing agent) at 150 °C for 20 min. Experimentation showed that the optimum thickness of the transferred metal shows that the optimum thickness is approximately 500 nm, which allows for a higher resistance to stresses. The successful transfer of copper, nickel and silver layers onto PDMS with a stronger adhesion force opens up many new applications dealing with the fabrication of flexible electrodes, sensors, and flexible soft magnets.