Shi-Li Zhang

Solid‐state nanopores (SSNPs) are of potential for a wide range of applications from single‐molecule detection and selective filtration to osmotic power harvesting and iontronics. As the demand for such applications escalates, a design scheme to sophisticate the nanopore platform is to integrate complementary nanofluidic components, including nanochannels and nanoreactors, to realize fully fletched lab‐on‐chip systems. Herein, we present a scalable fabrication strategy for planar SSNPs based on standard silicon technology that has been developed for advanced integrated circuits. We demonstrate a prototype device featuring a nanopore linking two microfluidic reservoirs, characterize its electrical noise profile, and quantify the streaming current generated under a pressure‐driven flow. Use of the silicon nanofabrication process further allows the geometry and dimension (length, width, height) of each planar nanopore to be independently designed and the nanopores to naturally become part of a fluidic system with mixed micro‐ and nanoscale channels on the same chip. This process supports wafer‐scale manufacture of high‐density micro/nanofluidics, delivers exceptional mechanical stability, and is fully compatible with complementary metal‐oxide‐semiconductor electronics. Together, these attributes establish a versatile, integrable nanofluidic platform for next‐generation sensing, energy, and analytical applications.

NbN is an attractive material for superconducting metallization of electronic devices due to its relatively high critical temperature of superconducting transition of 16 K. In this study, we demonstrate ion assisted reactive magnetron sputter deposition of superconducting NbN thin films directly on Si without the need for elevated deposition temperatures. The highest T _C achieved is 13 K. Two key factors determining the low temperature behavior are identified. The film morphology, specifically the density, influences the room temperature electron transport and the residual resistivity ratio. The degree of microstructural disorder, described as the crystallite size or microstrain, determines the critical temperature. Partial ionization of the film forming species results in both densification and increased crystallite size with beneficial impact on the film performance.

Upconversion nanoparticles (UCNPs) have attracted great interest due to their unique properties such as anti-Stokes shift, high biocompatibility, and photostability compared with other fluorophores. Single UCNP-based studies are important for highly sensitive biosensing and bioimaging. To enhance the photoluminescence (PL) intensity of UCNPs, various plasmonic nanostructures have been investigated in addition to engineering the elements and structures of UCNPs themselves. However, it is crucial but challenging to precisely control the position of a single UCNP relative to plasmonic nanostructures. Herein, gold nanorod dimers (GNRDs) are used to enhance the PL intensity of single UCNPs selectively captured in the gaps of GNRDs. The dimensions of GNRDs are designed with the assistance of COMSOL Multiphysics simulation to have a plasmonic resonance peak around the excitation wavelength for the UCNPs. After lithography-based fabrication of GNRDs and surface passivation, electron-beam induced deposition is used to selectively create carbon nanodomains (CNDs) in the gaps of GNRDs. The CNDs capture UCNPs by benefiting from the strong affinity between streptavidin and biotin. About 12% of the CNDs capture single UCNPs. Photoluminescence imaging shows an overall intensity enhancement by threefold for single UCNPs by GNRDs of 100 nm gap at 4×106 W/cm2 power density. This study shows a promising route for single UCNP-based studies, especially when it is needed to control the position of single UCNPs.

Extracellular vesicles (EVs) are nanoparticles encapsulated with a lipid bilayer, and they constitute an excellent source of biomarkers for multiple diseases. However, the heterogeneity in their molecular compositions constitutes a major challenge for their recognition and profiling, thereby limiting their application as an effective biomarker. A single-EV analysis technique is crucial to both the discovery and the detection of EV subpopulations that carry disease-specific signatures. Herein, a plasmonic nanohole array is designed for capturing single EVs and subsequently performing fluorescence detection of their membrane proteins by exploiting plasmonic amplification of the fluorescence signal. Unlike other reported methods, our design relies on an exclusive detection of single EVs captured inside nanoholes, thus allowing us to study only plasmonic effects and avoid other metal-induced phenomena while leveraging on the proximity of emitters to the plasmonic hotspots. The method is optimized through numerical simulations and verified by a combination of atomic force, scanning electron microscopy, and fluorescence microscopy. Fluorescence enhancement is then estimated by measuring the CD9 expression of small EVs derived from the human embryonic kidney (HEK293) cell line and carefully considering the spatial distribution of emission and excitation intensities. Fluorescence intensities of immunostained EVs show a moderate overall enhancement of intensity and follow the intensity trend predicted by simulation for nanohole arrays with different nanohole periods. Moreover, the number of observed EVs in the best-performing nanohole array increases by more than 12 times compared with EVs immobilized on a reference substrate, uncovering a vast amount of weakly fluorescent EVs that would remain undetected with the regular fluorescent method. Our nanohole array provides a basis for a future platform of single-EV analyses, also promising to capture the signature arising from low-expressing proteins.

Nanoscale sensors usually produce feeble signals susceptible to inevitable external interference. Several signal amplification solutions exist for mitigating the interference. However, most nanoscale sensors are fabricated on silicon-on-insulator (SOI) substrate, which is not compatible with the integration process of traditional vertical bipolar amplifiers. This work presents an ion-gated lateral bipolar amplifier that integrates a nanoribbon filed-effect transistor (NRFET) ion sensor with a lateral bipolar junction transistor (LBJT), all on an SOI substrate, thereby greatly simplifying the fabrication process. The direct connection between the LBJT base and the NRFET source enables immediate amplification of the NRFET signal, minimizing exposure to surrounding interference. Characterized by a peak current gain exceeding 20, this amplifier design leads to a 3–7-fold enhancement in the overall signal-to-noise ratio (SNR) compared to a reference NRFET. Furthermore, this gain in SNR is empirically validated during pH sensing applications. The possibility of substrate biasing makes the integrated LBJT-NRFET amplifier unique as it can independently tune the current gain and reduce the noise thereby improving the SNR performance.

Platinum silicide (PtSi) presents a promising superconductor for achieving silicon-based Josephson field-effect transistors (JoFETs). In a viable process flow to realize self-aligned PtSi formation, thermal oxidation at 600 °C is required to form a protective oxide layer on the surface of the as-formed PtSi selectively against Pt to facilitate subsequent selective etch in aqua regia. However, sub-10 nm PtSi films tend to agglomerate and even break into discrete PtSi islands upon thermal treatments above 500 °C. To achieve nanoscale JoFETs, we have developed a simple alternative with chemical oxidation at room temperature leading to the formation of homogeneous sub-5 nm PtSi films. The critical temperature of the resultant superconducting PtSi films is found to increase from 0.66 to 0.90 K when the PtSi thickness is raised from 3.1 to 12.7 nm, while, concurrently, the PtSi grains grow larger in thicker films. The critical temperature also increases from 0.53 to 0.66 K for the 3.1 nm PtSi film when the formation temperature is raised from 400 to 500 °C.

Tracing fast nanopore‐translocating analytes requires a high‐frequency measurement system that warrants a temporal resolution better than 1 µs. This constraint may practically shift the challenge from increasing the sampling bandwidth to dealing with the rapidly growing noise with frequencies typically above 10 kHz, potentially making it still uncertain if all translocation events are unambiguously captured. Here, a numerical simulation model is presented as an alternative to discern translocation events with different experimental settings including pore dimension, bias voltage, the charge state of the analyte, salt concentration, and electrolyte viscosity. The model allows for simultaneous analysis of forces exerting on a large analyte cohort along their individual trajectories; these forces are responsible for the analyte movement leading eventually to the nanopore translocation. Through tracing the analyte trajectories, the Brownian force is found to dominate the analyte movement in electrolytes until the last moment at which the electroosmotic force determines the final translocation act. The mean dwell time of analytes mimicking streptavidin decreases from ≈6 to ≈1 µs with increasing the bias voltage from ±100 to ±500 mV. The simulated translocation events qualitatively agree with the experimental data with streptavidin. The simulation model is also helpful for the design of new solid‐state nanopore sensors.

Fluorescence-based optical sensing techniques have continually been explored for single-molecule detection targeting myriad biomedical applications. Improving signal-to-noise ratio remains a prioritized effort to enable unambiguous detection at single-molecule level. Here, we report a systematic simulation-assisted optimization of plasmon-enhanced fluorescence of single quantum dots based on nanohole arrays in ultrathin aluminum films. The simulation is first calibrated by referring to the measured transmittance in nanohole arrays and subsequently used for guiding their design. With an optimized combination of nanohole diameter and depth, the variation of the square of simulated average volumetric electric field enhancement agrees excellently with that of experimental photoluminescence enhancement over a large range of nanohole periods. A maximum 5-fold photoluminescence enhancement is statistically achieved experimentally for the single quantum dots immobilized at the bottom of simulation-optimized nanoholes in comparison to those cast-deposited on bare glass substrate. Hence, boosting photoluminescence with optimized nanohole arrays holds promises for single-fluorophore-based biosensing.