Abstract The confinement of light into nanometer-sized (typically <10 nm) metallic nanogaps can generate extremely high near-field enhancement, dramatically boosting absorption, emission, and Raman scattering of target molecules situated within the gaps. However, the scarcity of cost-effective, reliable, and high-throughput nanofabrication techniques capable of fabricating sub-10 nm gaps, particularly in binary nanostructures, has significantly hindered their practical applications. Here, a high-throughput nanofabrication strategy that combines anodic aluminum oxide (AAO) templates, molecular self-assembly, and glancing-angle ion-beam etching (IBE) is proposed to controllably produce large-scale bimetallic gold–silver (Au–Ag) arrays with approximately 5 nm gaps. These arrays serve as exceptional surface-enhanced Raman spectroscopy (SERS) substrates, allowing for the ultrasensitive detection of target molecules with limits of detection (LODs) as low as 10–11 M for rhodamine 6G (R6G) and 4-mercaptobenzoic acid (4-MBA) and 10–8 M for bilirubin. The bimetallic Au–Ag nanogap arrays leverage the synergistic effects of gold’s strong absorption and silver’s superior plasmonic properties, achieving significantly enhanced electromagnetic fields compared to monolithic Au–Au nanogap arrays. This cost-effective and efficient nanofabrication approach overcomes the limitations of conventional methods for fabricating binary nanostructures, providing a viable solution for developing high-sensitive and reliable SERS-based detection platforms toward chemical-/bio-sensing.
Abstract Hydrazine (N2H4) is a widely used industrial chemical yet poses severe toxicity risks to human health and ecological systems. It is highly urgent to develop rapid, reliable, and accurate analytical methods for trace N2H4 monitoring. Surface-enhanced Raman spectroscopy (SERS) offers distinct advantages for trace analysis owing to its fingerprint specificity and ultrahigh sensitivity. However, conventional SERS strategies for hydrazine detection often suffer from poor signal reproducibility and unsatisfactory quantitative accuracy. Herein, we rationally construct a robust ratiometric SERS sensor for precise trace N2H4 determination by using highly stable gold@silver core–shell nanocubes (Au@AgNCs) as the enhancing substrate and 4-ethynylbenzaldehyde (4-EBA) as the specific recognition probe. The aldehyde group of 4-EBA selectively reacts with N2H4 via a Schiff-base reaction, generating a hydrazone product with a characteristic C═N Raman peak at 1533 cm–1. Crucially, the intrinsic Raman band of ethanol was employed as a built-in internal standard to effectively eliminate signal fluctuations caused by laser power drift, substrate inhomogeneity, and measurement variations, thereby significantly improving quantitative reliability and reproducibility. Density functional theory (DFT) calculations were further conducted to validate the sensing mechanism. The developed sensor exhibited excellent sensitivity, high selectivity, and good stability for N2H4 detection. Notably, it achieved strong anti-interference ability and reliable quantitative performance in real river water samples. This work provides a feasible and promising strategy for the on-site, accurate monitoring of toxic environmental pollutants.
Abstract The single-signal multistate conversion sensing mode not only improves detection sensitivity but also features a simple construction process and can effectively eliminate nonspecific signal interferences. The change of molecular structure and generation of new molecules are able to regulate the activation and inhibition of the resonance energy transfer (RET) mechanism more easily through the conversion of energy levels, thus realizing the on–off–on mode. In this work, a controlled release strategy was used to trigger the self-assembly of Bi2S3/BiOI heterojunctions via the release of Na2S, resulting from the specific recognition between carbohydrate antigen 242 (CA242) and its antibody. The formation of the Bi2S3/BiOI heterojunction changed the energy level of BiOI, thereby inhibiting the RET mechanism between the [Ru(dcbpy)3]Cl2 hydrogel (Ru-Hydrogel) and BiOI, and restoring the signal, achieving the on–off–on mode of the sensor. It was an effective method to directly relate the concentration of the target CA242 (10–4–103 U/mL) to the multistate conversion of the signal. The limit of detection of this sensor for CA242 reached 1.57 × 10–4 U/mL (S/N = 3), demonstrating high sensitivity. This study provided an innovative sensing strategy for fabricating electrochemiluminescence sensors in the on–off–on mode and offered a feasible method for the high-sensitivity detection of biomarkers in the analysis field.
Abstract The combination of capillary electrophoresis (CE) and electrochemistry, commonly in the form of amperometric detection (AD), has gained increasing importance by providing good selectivity, stability, and detection performance, especially when combined with non-aqueous media (NACE-AD). Despite these advantages, conventional NACE-AD systems face limitations when analyzing complex samples, being confronted with co-migrating analytes or the need for oxidative and reductive information at the same time. Established techniques for simultaneous oxidative and reductive detection often rely on complex electrode arrays, which are not able to provide completely independent electrode processes while posing complex electrochemical systems. To address these issues, a dual-detection concept (DDC) relying on dead-volume free flow splitting combined with two independent AD cells (CE-AD2) could provide a user-friendly alternative to existing approaches, avoiding most of these problems and giving new opportunities for method development. Moreover, dead-volume free flow splitting also allows other destructive, electroanalytical methods to be combined with CE-AD, e.g., voltammetry. The combination with linear-sweep voltammetry (LSV) offers a versatile tool for online identification of various analytes by their characteristic voltammogram (qualitative information) while using AD for quantitative information (CE-AD/LSV). This work presents two novel electrochemical DDCs for NACE using newly designed, synchronized, independent AD cells connected via a commercially available flow splitter. The first DDC, CE-AD2, simultaneously detects oxidizable and reducible species using independently optimized electrodes (platinum for oxidation and silver for reduction) and detection potentials within a single measurement run. The second approach, CE-AD/LSV, combines sensitive fixed-potential AD for quantification with LSV for online analyte identification. Together, these systems could improve flexibility, selectivity, and analytical performance for monitoring complex samples in NACE applications.
Abstract Point-of-care testing (POCT) plays a crucial role in both clinical- and home-based diagnostics. Integrated POCT systems that combine nucleic acid extraction with detection provide significant advantages, including portable operation, rapid processing, and high sensitivity. In this work, we present a fully automated and integrated nucleic acid detection system based on microfluidic chips with a surface-engraved rotary piston (SERP), which incorporates all of the liquid channels on the surface of one valve. This design consists of only three parts: the chip, the rubber sealing ring, and the rotary valve containing microfluidic channels, allowing the sequential connection of reaction chambers to facilitate nucleic acid extraction, recombinase polymerase amplification (RPA), and clustered regularly interspaced short palindromic repeats (CRISPR) into a single chip. Our chip consists of only three components, can be fabricated directly by 3D printing, and features a simple structure with a compact size. This platform was employed for the detection of human papillomavirus (HPV16) DNA, achieving a limit of detection (LOD) as low as 60 copies/mL. This result underscores the potential of the SERP as a rapid, cost-effective, and modular solution for POCT applications.
