Enzyme-Assist-Interference-Free Strategy for Raman Selective Determination of Sialic Acid

Glucose sandwich assay based on surface-enhanced Raman spectroscopy

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

Plasmonic Array at the Liquid-Liquid Interface: A Dual-Mode Optical Sensing Platform for Multianalytes

Analyte-triggered nanoparticle (NP) assemblies in bulk colloidal suspension have been extensively utilized in various optical sensors. Nevertheless, the assembling process is still limited by the slow diffusion dynamics of NPs and the low concentration of analytes in trace detections, which hinders further improvement of the sensitivity and repeatability of the sensors. In this work, by functionalizing the gold NPs with specific ligands, we constructed a dual-mode optical sensing platform for multianalytes based on the plasmonic NP array at the liquid-liquid interface. Through emulsification, the NP diffusion kinetics are boosted for several orders, and the NPs are condensed from the bulk aqueous phase to the liquid-liquid interface as a plasmonic array. The as-formed metasurface generates major reflectance and surface-enhanced Raman scattering changes in response to analytes, providing two optical sensing modes. As prototypes, cysteine and glucose are selected as the target molecules, achieving the limit of detection as 193 ± 2 and 297 ± 12 pM, respectively.

Quantitative and Noninvasive Detection of SAH-Related MiRNA in Cerebrospinal Fluids In Vivo Using SERS Sensors Based on Acupuncture-Based Technology

Quantitative analysis of microRNAs (miRNAs) in a noninvasive manner is of vital importance for disease diagnosis and prognosis evaluation. However, conventional strategies for realizing accurate, simple, and sensitive detection of target molecules are still a challenge, especially for miRNAs due to their low abundance and susceptibility in the complex biological environment. Here, a novel surface-enhanced Raman scattering (SERS) strategy was established for quantitative detection and monitoring of miRNA-21-5p (miR-21-5p) in living cells and in vivo cerebrospinal fluid (CSF) by applying hairpin DNA (hpDNA)-conjugated gold nanostars (GNSs) SERS probes combined with acupuncture-based technology. This strategy enabled ultrasensitive exploration toward miR-21-5p in a wide range from 1 fM to 100 pM in cell lysates. Moreover, SERS analysis facilitated the detection and long-term monitoring for in vivo miR-21-5p noninvasively. This developed strategy promises to offer a powerful method for the analysis of multiple biomolecules in single cells and living bodies.

Nanopore-Based Single-Entity Electrochemistry for the Label-Free Monitoring of Single-Molecule Glycoprotein-Boronate Affinity Interaction and Its Sensing Application

Nanopipettes provide a promising confined space that enables advances in single-molecule analysis, and their unique conical tubular structure is also suitable for single-cell analysis. In this work, functionalized-nanopore-based single-entity electrochemistry (SEE) analysis tools were developed for the label-free monitoring of single-molecule glycoprotein-boronate affinity interaction for the first time, and immunoglobulin G (IgG, one of the important biomarkers for many diseases such as COVID-19 and cancers) was employed as the model glycoprotein. The principle of this method is based on a single glycoprotein molecule passing through 4-mercaptophenylboronic acid (4-MPBA)-modified nanopipettes under a bias voltage and in the meantime interacting with the boronate group from modified 4-MPBA. This translocation and affinity interaction process can generate distinguishable current blockade signals. Based on the statistical analysis of these signals, the equilibrium association constant (κ_a) of single-molecule glycoprotein-boronate affinity interaction was obtained. The results show that the κ_a of IgG in the confined nanopore at the single-molecule level is much larger than that measured in the open system at the ensemble level, which is possibly due to the enhanced multivalent synergistic binding in the restricted space. Moreover, the functionalized-nanopore-based SEE analysis tools were further applied for the label-free detection of IgG, and the results indicate that our method has potential application value for the detection of glycoproteins in real samples, which also paves way for the single-cell analysis of glycoproteins.

Triple-Function Au-Ag-Stuffed Nanopancakes for SERS Detection, Discrimination, and Inactivation of Multiple Bacteria

New strategies combining sensitive pathogenic bacterial detection and high antimicrobial efficacy are urgently desirable. Here, we report smart triple-functional Au-Ag-stuffed nanopancakes (AAS-NPs) exhibiting (1) controllably oxidative Ag-etching thickness for simultaneously obtaining the best surface-enhanced Raman scattering (SERS) enhancement and high Ag-loading antibacterial drug delivery, (2) expressive Ag⁺-accelerated releasing capability under neutral phosphate-buffered saline (PBS) (pH ∼ 7.4) stimulus and robust antibacterial effectiveness involving sustainable Ag⁺ release, and (3) three-in-one features combining specific discrimination, sensitive detection, and inactivation of different pathogenic bacteria. Originally, AAS-NPs were synthesized by particle growth of the selective Ag-etched Au@Ag nanoparticles with K₃[Fe(CN)₆], followed by the formation of an unstable Prussian blue analogue for specifically binding with bacteria through the cyano group. Using specific bacterial "fingerprints" resulting from the introduction of dual-function 4-mercaptophenylboronic acid (4-MPBA, serving as both the SERS tag and internal standard) and a SERS sandwich nanostructure that was made of bacteria/SERS tags/AAS-NPs, three bacteria (E. coli, S. aureus, and P. aeruginosa) were highly sensitively discriminated and detected, with a limit of detection of 7 CFU mL^-1. Meanwhile, AAS-NPs killed 99% of 1 × 10⁵ CFU mL^-1 bacteria within 60 min under PBS (pH ∼ 7.4) pretreatment. Antibacterial activities of PBS-stimulated AAS-NPs against S. aureus, E. coli, and P. aeruginosa were extraordinarily increased by 64-fold, 72-fold, and 72-fold versus PBS-untreated AAS-NPs, respectively. The multiple functions of PBS-stimulated AAS-NPs were validated by bacterial sensing, inactivation in human blood samples, and bacterial biofilm disruption. Our work exhibits an effective strategy for simultaneous bacterial sensing and inactivation.