Rapid prototyping of polydimethylsiloxane (PDMS) microchips using electrohydrodynamic jet printing: Application to electrokinetic assays

Polydimethylsiloxane (PDMS) based microfluidic devices have found increasing utility for electrophoretic and electrokinetic assays because of their ease of fabrication using replica molding. However, the fabrication of high-resolution molds for replica molding still requires the resource-intensive and time-consuming photolithography process, which precludes quick design iterations and device optimization. We here demonstrate a low-cost, rapid microfabrication process, based on electrohydrodynamic jet printing (EJP), for fabricating non-sacrificial master molds for replica molding of PDMS microfluidic devices. The method is based on the precise deposition of an electrically stretched polymeric solution of polycaprolactone in acetic acid on a silicon wafer placed on a computer-controlled motion stage. This process offers the high-resolution (order 10 $\mu$m) capability of photolithography and rapid prototyping capability of inkjet printing to print high-resolution templates for elastomeric microfluidic devices within a few minutes. Through proper selection of the operating parameters such as solution flow rate, applied electric field, and stage speed, we demonstrate microfabrication of intricate master molds and corresponding PDMS microfluidic devices for electrokinetic applications. We demonstrate the utility of the fabricated PDMS microchips for nonlinear electrokinetic processes such as electrokinetic instability and controlled sample splitting in ITP. The ability to rapid prototype customized reusable master molds with order 10 $\mu$m resolution within a few minutes can help in designing and optimizing microfluidic devices for various electrokinetic applications.     

A Novel Electroanalytical Biosensor Based on ZIF-8/Acetylcholinesterase Bio-nanohybrids for Early Management of Hirschsprung Disease

Hirschsprung's disease (HD) is characterised by missing nerve cells in the colon of infants and children which results in strained bowel movement. Under such situations, undiagnosed and untreated cases often lead to a cascade of gastrointestinal infections eventually resulting in Hirschsprung-assisted enterocolitis which has significantly high mortality rate. This is further exacerbated by the absence of suitable, sensitive and efficient technologies to detect the pathological segment of the intestine, which could significantly reduce surgery duration in the operation theatre, as well as associated risks to patients. It therefore becomes a matter of extreme importance to develop a point-of-care platform for early and efficient management/identification of the occurrence of HD in neonates and older children during its onset, before it proves fatal with life-threatening outcomes. The present work reports an electrochemical enzymatic biosensor using Zeolitic Imidazolate Framework-8 (ZIF-8) modified with acetylcholinesterase enzyme (AchE), for detection of HD as a function of the key biomarker – acetylcholine. The developed sensor was initially characterized using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), while the analytical performance and insights onto interfacial redox kinetics were assessed using Differential Pulse Voltammetry (DPV) and EIS respectively. The sensor exhibited limit of detection and sensitivity of 0.19 μM and sensitivity of 0.42 μA/μM/mm² with a shelf life of 1 month, while remaining unperturbed in the presence of common interferants. The performance of developed sensor was also examined in spiked serum samples and was observed to yield a high degree of linearity.