Nanofabricated pores in 20 nm-thick silicon nitride membranes were used to probe various protein analytes as well as to perform an antigen−antibody binding assay. A two-compartment electrochemical cell was separated by a single nanopore, 28 nm in diameter. Adding proteins to one compartment caused current perturbations in the ion current flowing through the pore. These perturbations correlated with both the charge and the size of the protein or of a protein−protein complex. The potential of this nanotechnology for studying protein−protein interactions is highlighted with the sensitive detection of β-human chorionic gonadotropin, a hormone and clinical biomarker of pregnancy, by monitoring in real time and at a molecular level the formation of a complex between hormones and antibodies in solution. In this form, the assay compared advantageously to immunoassays, with the important difference that labels, immobilization, or amplification steps were no longer needed. In conclusion, we present proof-of-principle that properties of proteins and their interactions can be investigated in solution using synthetic nanopores and that these interactions can be exploited to measure protein concentrations accurately.

We report the detection of protein molecules with nanofabricated pores using the resistive pulse sensing method. A $20\text{-}\mathrm{nm}$ -thick silicon nitride membrane with a nanofabricated pore measuring about $55\mathrm{nm}$ in diameter separated an electrolyte cell into two compartments. Current spike trains were observed when bovine serum albumin (BSA) was added to the negatively biased compartment. The magnitude of the spikes corresponded to particles $7–9\mathrm{nm}$ in diameter (the size of a BSA molecule) passing through the pore. This suggests that the current spikes were current blockages caused by single BSA molecules. The presented nano-Coulter counting method could be applied to detect single protein molecules in free solution, and to study the translocation of proteins through a pore.

MEMS inductors are used in a wide range of applications in micro- and nanotechnology, including RF MEMS, sensors, power electronics, and Bio-MEMS. Fabrication technologies set the boundary conditions for inductor design and their electrical and mechanical performance. This review provides a comprehensive overview of state-of-the-art MEMS technologies for inductor fabrication, presents recent advances in 3D additive fabrication technologies, and discusses the challenges and opportunities of MEMS inductors for two emerging applications, namely, integrated power electronics and neurotechnologies. Among the four top-down MEMS fabrication approaches, 3D surface micromachining and through-substrate-via (TSV) fabrication technology have been intensively studied to fabricate 3D inductors such as solenoid and toroid in-substrate TSV inductors. While 3D inductors are preferred for their high-quality factor, high power density, and low parasitic capacitance, in-substrate TSV inductors offer an additional unique advantage for 3D system integration and efficient thermal dissipation. These features make in-substrate TSV inductors promising to achieve the ultimate goal of monolithically integrated power converters. From another perspective, 3D bottom-up additive techniques such as ice lithography have great potential for fabricating inductors with geometries and specifications that are very challenging to achieve with established MEMS technologies. Finally, we discuss inspiring and emerging research opportunities for MEMS inductors.