Tunable Preparation of SERS-Active Au-Ag Janus@Au NPs for Label-Free Staphylococcal Enterotoxin C Detection

A colorimetric/SERS dual-mode sensor based on ferric ion-dopamine@Au-Ag-Au Janus NPs for acrylamide determination in baked goods

This study successfully developed a colorimetric/SERS dual-mode sensor for determining acrylamide in baked goods based on the excellent peroxidase-like activity and Raman activity of Fe-PHS@Au-Ag-Au Janus NPs. In colorimetric mode, the thiol-ene Michael addition between acrylamide (AA) and glutathione (GSH) efficiently eliminates GSH-induced peroxidase-like activity inhibition. The peroxidase-like activity of Fe-PHS@Au-Ag-Au Janus NPs gradually recovered, and the blue color of the solution gradually deepened with the increase in AA dosage. In surface-enhanced Raman spectroscopy (SERS), Apt-Fe-PHS@Au-Ag-Au Janus NPs can selectively capture AA and bind specifically, leading to the dissociation of Apt and Fe-PHS@Au-Ag-Au Janus NPs. The Raman activity of Apt-Fe-PHS@Au-Ag-Au Janus NPs decreases due to the dissociation of Apt. The dual-mode sensor was utilized for the determination of acrylamide in the concentrations range from 0.05 to 20 µg·L-1 with detection limits of 0.06 µg·L-1 (SERS) and 0.01 µg·L-1 (colorimetric). The recovery in baked samples was between 91.0 and 108.0%.

A probe-mediated fluorescent biosensor for MC-LR detection using exonuclease III as a signal amplifier

Microcystin-lr (MC-LR) is one of the most toxic and ubiquitous microcystins (MCs) released by cyanobacteria. Exposure to MC-LR can cause multiple organ damage and even death of the organism. Therefore, creating highly sensitive and dependable methods for detecting trace MC-LR is crucial. Herein, we developed a novel fluorescence aptasensor aided by exonuclease III (Exo III) for the highly sensitive detection of MC-LR. In the presence of MC-LR, the affinity interaction between MC-LR and aptamer A was triggered, leading to the release of blocker B. This unbound blocker can initiate Exo III-mediated signal amplification to digest the probe H, thereby recovering the fluorescence signal for readout. The proposed Exo III-assisted sensing platform demonstrated remarkable sensitivity and selectivity, achieving a limit of detection (LOD) of 0.37 ng L-1. Furthermore, it is robust and has been effectively utilized on water samples, achieving acceptable recovery rates (95.04-107.01%). With excellent sensitivity, high selectivity, efficient signal amplification, and fluorescence readout, the proposed biosensor offered a new and reliable alternative for the detection of trace MC-LR in the environment and the early warning of algal toxins.

A SERS "on-off" sensor for Hg2+ and fumonisin B1 determination in grains based on Au-Janus Ag NPs modified by carbon dots

Se-WCDs-Au-Janus Ag NPs with weak oxidase activity were synthesized using Se-W carbon dots (Se-WCDs) as stabilizers and reducing agents. These Janus nanoparticles (Janus NPs) effectively catalyze the reduction of mercury ions (Hg2+) to metallic mercury (Hg0), generating Au-Ag-Hg mercury alloys (Au-Ag@HgNPs). The aggregated Au-Ag@HgNPs on the nanoparticles improve the SERS activity of Se-WCDs-Au-Janus Ag NPs through a synergistic effect of electromagnetic enhancement and chemical enhancement. Interestingly, adding FB1 turns off the Raman signal by inhibiting the aggregation of Au-Ag@HgNPs. Based on these findings, a SERS "on-off" sensor utilizing the Se-WCDs-Au-Janus Ag NPs as the probe was successfully developed to determine fumonisin B1 (FB1) and Hg2+ in grains. The detection limits were as low as 0.005 μg·L-1 for Hg2+ and 0.006 μg·L-1 for FB1.

AFB1-responsive mesoporous silica nanoparticles for AFB1 quantification based on aptamer-regulated release of SERS reporter

In this study, we propose a novel surface-enhanced Raman scattering (SERS) method for quantifying aflatoxin B1 (AFB1). This method relies on the target-triggered release of a SERS reporter from aptamer-sealed aminated mesoporous silica nanoparticles (MSNs). These MSNs were synthesized to accommodate 4-mercaptophenylboronic acid (4-MPBA) within their well-defined micropores, which were subsequently sealed with AFB1 aptamers. Upon specific binding of AFB1 to its aptamer, the conformational change in the aptamer is regulated by the presence of the target. Consequently, a positive linear relationship between the AFB1 concentration and the 4-MPBA SERS signal was observed. Under optimal conditions, the method exhibited a good linear relationship over the range of 0.1 to 5 ng/mL AFB1, with a limit of detection (LOD) of 0.03 ng/mL. This strategy was validated using wheat samples, yielding results comparable to high performance liquid chromatography-fluorescence detector (P > 0.05), confirming its reliability for detecting AFB1 in complex food matrices.

High sensitivity chemiluminescence enzyme immunoassay for detecting staphylococcal enterotoxin C1 and its application in multi-matrices

Staphylococcal enterotoxins (SEs) serve as the primary cause of staphylococcal food poisoning and other foodborne intoxications. Among them, staphylococcal enterotoxin C (SEC) has the highest prevalence in dairy products, leading to multiple outbreaks all around the world. Thus, it is of great significance to develop a highly sensitive, highly specific and easy to operate chemiluminescent sandwich enzyme immunoassay (CLEIA) for detecting staphylococcal enterotoxin C (SEC1). We selected two pairs of anti-SEC1 monoclonal antibodies (mAbs) (SEC1-G8 and SEC1-C4), and a chemiluminescent sandwich enzyme immunoassay (CLEIA) was constructed. This approach can detect SEC1 within a concentration spectrum of 3.2-4000 pg/mL, with the detection limit being 2.1 pg/mL. At three concentrations (3.2, 20, and 400 pg/mL), both the intra- and inter-assay coefficient variations were coming in at 6.31 % and 11.2 % respectively. No cross-reaction was noticed in the SEA, SEB, and SED tests. SEC1 was successfully detected by employing the CLEIA method in spiked matrices and commercial samples, and the average recovery rate ranges from 81.6 % to 108.1 %. Therefore, the highly sensitive, SEC1- specific, and easy-to-operate CLEIA could be a useful tool in the near future for quantifying SEC1 in public health and food safety.

SERS aptasensor detection of aflatoxin B1 based on silicon-au-ag Janus nanocomposites

Aflatoxin B1 (AFB1) is a prevalent contaminant in maize, posing significant threats to human health. This study designed AuAg Janus NPs with intrinsic Raman signals as signal probes and SiO2@AgNPs as capture probes. The two were coupled through complementary base pairing to ensure the ordered, controlled distribution of noble metal nanoparticles. The AuAg Janus NPs and the highly stable SiO2 carrier is expected to avoid the adverse effects on stability caused by using signal molecules and the formation of random aggregates when using the noble metal nanoparticle gap effect to concentrate on the electromagnetic field. This study improved the negative impact of AgNPs' high surface energy on their uniformity, while enhancing the pH adaptability of AuAg Janus NPs. In the presence of AFB1, the composite disintegrates, and the SERS intensity showed a negative correlation with AFB1 concentration, enabling highly sensitive and stable detection of AFB1.

Non-invasive detection of systemic lupus erythematosus using SERS serum detection technology and deep learning algorithms

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple symptoms, and its rapid screening is the research focus of surface-enhanced Raman scattering (SERS) technology. In this study, gold@silver-porous silicon (Au@Ag-PSi) composite substrates were synthesized by electrochemical etching and in-situ reduction methods, which showed excellent sensitivity and accuracy in the detection of rhodamine 6G (R6G) and serum from SLE patients. SERS technology was combined with deep learning algorithms to model serum features using selected CNN, AlexNet, and RF models. 92 % accuracy was achieved in classifying SLE patients by CNN models, and the reliability of these models in accurately identifying sera was verified by ROC curve analysis. This study highlights the great potential of Au@Ag-PSi substrate in SERS detection and introduces a novel deep learning approach for SERS for accurate screening of SLE. The proposed method and composite substrate provide significant value for rapid, accurate, and noninvasive SLE screening and provide insights into SERS-based diagnostic techniques.

Morphology and optical properties of Au-Ag hybrid nanoparticles regulation and its ultra-sensitive SERS immunoassay detection in carbohydrate antigen 19-9

The development of an ultra-sensitive detection method for carbohydrate antigen 19-9 (CA19-9) is very important for the early diagnosis of pancreatic cancer. In this work, we developed a new strategy to achieve a variety of Au-Ag hybrid nanoparticles from janus to core-satellite which is controlled by the volume of AgNO3 and the concentration of benzimidazolecarboxylic acid (MBIA). With the volume of AgNO3 increased, Au-Ag hybrid nanoparticles changed from janus to core-satellite and the characteristic absorption peak showed two opposite trends. The size and number of Ag islands were determined by the concentration of MBIA. Au-Ag core-satellites nanoparticles with a large number of small-sized Ag have the highest SERS intensity. Then we used them as SERS nanotags and Au-Polystyrene nanospheres modified by captured anti-CA19-9 antibody as solid substrates to realize the ultra-sensitive detection of CA19-9 with a low limit of detection of 1.25 × 10-6 IU/mL and a wide linear range of 1.00 × 10-5 -1.00 × 104 IU/mL. This work not only demonstrates that MBIA and AgNO3 were the key factors in the growth of Au-Ag hybrid nanoparticles from 2D to 3D structure but also supplies an ultra-sensitive detection method for CA19-9 which has a potential practicability in the clinical early diagnoses of pancreatic cancer.

Exclusive Core-Janus Satellite Assembly Based on Au-Ag Janus Self-Aligned Distributions with Abundant Hotspots for Ultrasensitive Detection of CA19-9

The development of surface-enhanced Raman scattering (SERS) probes with high sensitivity and stability is imminent to improve the accuracy of cancer diagnosis. Here, an exclusive core-Janus satellite (CJS) assembly was constructed by a hierarchical assembly strategy in which the Au-Ag Janus satellite is vertically self-aligned on the core surface. In the process, a silica shell template was ingeniously employed to asymmetrically mask the presatellites for the in situ formation of the Janus structure, and a series of Janus satellites with different morphologies were developed by regulating the encapsulated area of the presatellites. The ordered-oriented arrangement of Au-Ag Janus and unique heterojunction morphology permit CJS assemblies, featuring two types of plasmonic nanogaps, including intrananocrevices for individual Janus and internanogaps between neighboring Janus, thereby multiplying the "hotspots" compared to conventional core-monotonous satellites, which contributes to superior SERS activity. As anticipated, the enhancement factor of CJS assemblies was as high as 3.8 × 108. Moreover, it is intriguing that the directional distribution and head physically immobilized by Janus provided uniform and stable SERS signals. The SERS probe based on the CJS assembly for the detection of carbohydrate antigen 19-9 resulted in an ultrahigh sensitivity with a limit of detection of 3.7 × 10-5 IU·mL-1, which is nearly 10 times lower than other SERS probes, and a wide detection range of 3 × 10-5 to 1 × 104 IU·mL-1. The CJS assembly with excellent SERS performance is promising to advance further development of the early diagnosis of pancreatic cancer.