Visual and quantitative lateral flow immunoassay based on Au@PS SERS tags for multiplex cardiac biomarkers.

Rapid and sensitive detection of multiple biomarkers by lateral flow immunoassay (LFIA) remains challenging for signal amplification for commonly used nanotags. Herein, we report a novel LFIA strip for visual and highly sensitive analysis of two cardiac biomarkers based on functionalized gold nanoparticles @ polystyrene microsphere (Au@PS）microcavity as surface-enhanced Raman scattering (SERS) tags. Antibody-modified Au@PS was designed as a SERS label. The evanescent waves propagating along the surface of the PS microcavity and the localized surface plasmons of the gold nanoparticles were coupled to enhance the light-matter interaction synergistically for Raman signal enhancement. In this strategy, the proposed Au@PS SERS tags-based LFIA was carried out to quantify the content of the heart failure and infarct biomarkers synchronously within 15 min and get the limits of detection of 1 pg/mL and 10 pg/mL for cardiac troponin I (cTnI) and N-terminal natriuretic peptide precursor (NT-proBNP), respectively. The results demonstrated 10-20 folds more sensitivity than that of the standard colloidal gold strip and fluorescent strip for the same biomarkers. This novel quantitative LFIA shows promise as a high-sensitive and visual sensing method for relevant clinical and forensic analysis.

Plasmon-coupled microcavity aptasensors for visual and ultra-sensitive simultaneous detection of Staphylococcus aureus and Escherichia coli.

Septicemia and bacteremia are serious infections in the bloodstream. Thus, time-saving and ultra-sensitive pathogenic bacteria detection is highly required. Herein, we constructed gold nanoparticle-modified polystyrene microspheres (Au/PS) as plasmon-coupled microcavities to realize simultaneous detection of Staphylococcus aureus and Escherichia coli based on a fluorescence and surface-enhanced Raman spectroscopy (SERS) dual-mode method. Fluorescence imaging, serving as a means for assistant validation and rapid screening, was carried out to achieve qualitative and semi-quantitative determination, which gave us visual information of the existence and distribution of the target bacteria. Meanwhile, SERS test was conducted to realize ultra-sensitive quantitative detection. The evanescent wave aroused from total internal reflection in PS microcavities coupled with the localized electromagnetic field from surface plasmons of gold nanoparticles to improve light-matter interaction synergistically, leading to an enhancement factor of 2.25 × 1011 for SERS sensing. The whole measurement was carried out in a typical sandwich assay of "capture probe-target bacteria-signal probe." As a result, calibrated concentration response curves demonstrated the sensitive quantitative detection with the limit of detection (LOD) of 3 cfu/mL for S. aureus and 2 cfu/mL for E. coli. This rapid, ultra-sensitive, and visual sensing method was further developed for dual-bacteria detection in the whole blood samples.

CdS quantum dots/Au nanoparticles/ZnO nanowire array for self-powered photoelectrochemical detection of Escherichia coli O157:H7.

In this paper, the hydrothermally grown ZnO nanowire array (NWs) was modified by Au nanoparticles (NPs) and CdS quantum dots (QDs) to construct a high-performance photoelectrochemical (PEC) electrode. The aligned ZnO NWs, which decorated Au NPs and CdS QDs have the effective light absorption range from UV to visible region. This hybrid structure provided a self-powered PEC electrode with a favorable energy-band configuration for fast charge separation and transportation. Meanwhile, the Au NPs and CdS QDs also made increase of the surface area to improve the immobilization of the analytes. After assembling aptamer as recognition element, this composite nanoarray was further developed as a self-powered PEC biosensor by synergizing above multiple enhancement factors. The PEC aptasensor exhibited a rapid response in a wide linear range of 10-107 CFU/mL with the detection limit as low as 1.125 CFU/mL to Escherichia coli O157:H7 (E. coli O157:H7). This approach would offer an alternative PEC transduction for fast environment monitoring and clinical diagnosis related to pathogenic bacteria.