Multifunctional Au nano-bridged nanogap probes as ICP-MS/SERS dual-signal tags and signal amplifiers for bacteria discriminating, quantitative detecting and photothermal bactericidal activity

Highly sensitive detection of Salmonella typhimurium via gold and magnetic nanoparticle-mediated sandwich hybridization coupled with ICP-MS

Foodborne pathogens including Salmonella typhimurium (S. typhimurium) are responsible for over 600 million global incidences of illness annually, posing a significant threat to public health. Inductively coupled plasma mass spectrometry (ICP-MS), coupled with element labeling strategies, has emerged as a promising platform for multivariate and accurate pathogen detection. However, achieving high specificity and sensitivity remains a critical challenge. Herein, we synthesize clustered magnetic nanoparticles (MNPs) and popcorn-shaped gold nanoparticles (AuNPs) to conjugate capture and report DNA probes for S. typhimurium, respectively. These engineered nanoparticles facilitate the identification of S. typhimurium DNA through a sandwich hybridization technique. ICP-MS quantification of Au within the sandwich-structure complexes allows for precise S. typhimurium detection. The unique morphology of the AuNPs and MNPs increases the available sites for probe attachment, enhancing the efficiency of S. typhimurium DNA capture, broadening the detection range to 101-1010 copies mL-1, and achieving a low detection limit of 1 copy mL-1, and the overall assay time is 70 min. The high specificity of this method is verified by anti-interference assays against ten other pathogens. The recovery was 96.8-102.8% for detecting S. typhimurium DNA in biological samples. As these specially designed nanoparticles may facilitate the attachment of various proteins and nucleic acid probes, they may become an effective platform for detecting multiple pathogens.

Pathogen detection via inductively coupled plasma mass spectrometry analysis with nanoparticles

Infections caused by viruses and bacteria pose a significant threat to global public health, emphasizing the critical importance of timely and precise detection methods. Inductively coupled plasma mass spectrometry (ICP-MS), a contemporary approach for pathogen detection, offers distinct advantages such as high sensitivity, a wide linear range, and multi-index capabilities. This review elucidates the underexplored application of ICP-MS in conjunction with functional nanoparticles (NPs) for the identification of viruses and bacteria. The review commences with an elucidation of the underlying principles, procedures, target pathogens, and NP requirements for this innovative approach. Subsequently, a thorough analysis of the advantages and limitations associated with these techniques is provided. Furthermore, the review delves into a comprehensive examination of the challenges encountered when utilizing NPs and ICP-MS for pathogen detection, culminating in a forward-looking assessment of the potential pathways for advancement in this domain. Thus, this review contributes novel perspectives to the field of pathogen detection in biomedicine by showcasing the promising synergy of ICP-MS and NPs.

A colorimetric and SERS dual-mode aptasensor for the detection of Shiga toxin type II based on Mn/Fe-MIL(53)@AuNSs

Shiga toxin type II (Stx2), the major virulence component of enterohemorrhagic Escherichia coli, is strongly associated with the life-threatening hemolytic uremic syndrome thus posing a substantial risk to food safety and human health. In this work, a dual-mode aptasensor with colorimetric and surface-enhanced Raman scattering was developed for Stx2 specific detection based on noble metal nanoparticles and Raman reporter loaded metal-organic framework (Mn/Fe-MIL(53)@AuNSs-MBA). The Mn/Fe-MIL(53)@AuNSs could catalyze the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), thereby enabling visual detection. Meanwhile, the SERS signal from MBA can be enhanced by the decorated AuNSs. Under optimal conditions, a linear range of 0.05-500 ng/mL with limit of detection (LOD) of 26 pg/mL was achieved in colorimetric mode and a linear range of 5-1000 ng/mL with LOD of 0.82 ng/mL in SERS mode, in which the dual-mode results complement each other, widening the linear range, increasing the accuracy and reliability of the detection. The method was further applied to the detection of Stx2 in milk with average recovery of 101.1 %, demonstrating its superior potential for bacterial toxin monitoring.

ICP-MS and fluorescence dual-mode detection of ZIKV-RNA based on quantum dot labeling with hybridization chain reaction

The detection of Zika virus (ZIKV) is of great significance to human life and health. Herein, we presented an ICP-MS and fluorescent dual-mode sensor for quantitative analysis of Zika virus RNA fragments (ZIKV-RNA), which employed quantum dots (QDs) as signal tags and combined with hybridization chain reaction (HCR). The dual-mode sensor realized cross-checking of the analysis results and improved the assay accuracy. Firstly, the single-stranded DNA (ssDNA) was anchored on the surface of magnetic beads (MBs). Afterward, HCR was conducted with probe DNA-CdSe quantum dots conjugates (pDNA-QDs) and link DNA (lDNA), producing the MBs-ssDNA-[pDNA-QDs-lDNA]n conjugates. In the presence of target ZIKV-RNA, a strand displacement reaction occurred, leading to the dissociation of the [pDNA-QDs-lDNA]n labels from the conjugates into the solution. Finally, the signal intensity was detected using ICP-MS and fluorescence analysis, with achieved limits of detection of 131 pM and 152 pM, respectively. The inter-assay RSD values of fluorescence and ICP-MS were 3.94 % and 4.26 % at 10 nM level, respectively, showing that the method had good precision. This method showed high selectivity and was applied to the analysis of biological fluids. There was no significant difference between the results of ICP-MS modes and fluorescence mode. This method offers a new strategy for sensitivity analysis of ZIKV-RNA and exhibits promise in clinical applications for diagnosis.

A novel strategy for specific sensing and inactivation of Escherichia coli: Constructing a targeted sandwich-type biosensor with multiple SERS hotspots to enhance SERS detection sensitivity and near-infrared light-triggered photothermal sterilization performance

Human health is greatly threatened by bacterial infection, which raises the risk of serious illness and death in humans. For early screening and accurate treatment of bacterial infection, there is a strong desire to undertake ultrasensitive detection and effective killing of pathogenic bacteria. Herein, a novel surface-enhanced Raman scattering (SERS) biosensor based on sandwich structure consisting of capture probes/bacteria/SERS tags was established for specific identification, capture and photothermal killing of Escherichia coli (E. coli). Finite-difference time-domain (FDTD) technique was used to simulate the electromagnetic field distribution of capture probes, SERS tags and sandwich-type SERS substrate, and a possible SERS enhancement mechanism based on sandwich structure was presented and discussed. Sandwich-type SERS biosensor successfully achieved distinctive identification and magnetic beneficiation of E. coli. In addition, a single SERS substrate, including capture probes and SERS tags, could also achieve outstanding photothermal effects as a consequence of localized surface plasmon resonance (LSPR) effect. Intriguingly, sandwich-type SERS biosensor demonstrated a higher photothermal conversion efficiency (50.03 %) than the single substrate, which might be attributed to the formation of target bacterial clusters. The superior biocompatibility and the low toxicity of the sandwich-type biosensor were confirmed. Our approach offers a fresh method for constructing sandwich-type biosensor with multiple SERS hotspots based on extremely effective hybrid plasmonic nanoparticles, and has a wide range of potential applications in the recognition and treatment of bacteria.

Advances in signal amplification strategies applied in pathogenic bacteria apta-sensing analysis-A review

Pathogenic bacteria are primarily kinds of food hazards that provoke serious harm to human health via contaminated or spoiled food. Given that pathogenic bacteria continue to reproduce and expand once they contaminate food, pathogenic bacteria of high concentration triggers more serious losses and detriments. Hence, it is essential to detect low-dose pollution at an early stage with high sensitivity. Aptamers, also known as "chemical antibodies", are oligonucleotide sequences that have attracted much attention owing to their merits of non-toxicity, small size, variable structure as well as easy modification of functional group. Aptamer-based bioanalysis has occupied a critical position in the field of rapid detection of pathogenic bacteria. This is attributed to the unique advantage of using aptamers as recognition elements in signal amplification strategies. The signal amplification strategy is an effective means to improve the detection sensitivity. Some diverse signal amplification strategies emphasize the synthesis and assembly of nanomaterials with signal amplification capabilities, while others introduce various nucleic acid amplification techniques into the detection system. This review focuses on a variety of signal amplification strategies employed in aptamer-based detection approaches to pathogenic bacteria. Meanwhile, we provided a detailed introduction to the design principles and characteristics of signal amplification strategies, as well as the improvement of sensor sensitivity. Ultimately, the existing issues and development trends of applying signal amplification strategies in apta-sensing analysis of pathogenic bacteria are critically proposed and prospected. Overall, this review discusses from a new perspective and is expected to contribute to the further development of this field.

Development of a Magnetically-Assisted SERS Biosensor for Rapid Bacterial Detection

Introduction

Ultrasensitive bacterial detection methods are crucial to ensuring accurate diagnosis and effective clinical monitoring, given the significant threat bacterial infections pose to human health. The aim of this study is to develop a biosensor with capabilities for broad-spectrum bacterial detection, rapid processing, and cost-effectiveness.

Methods

A magnetically-assisted SERS biosensor was designed, employing wheat germ agglutinin (WGA) for broad-spectrum recognition and antibodies for specific capture. Gold nanostars (AuNSs) were sequentially modified with the Raman reporter molecules and WGA, creating a versatile SERS tag with high affinity for a diverse range of bacteria. Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) antibody-modified Fe3O4 magnetic gold nanoparticles (MGNPs) served as the capture probes. Target bacteria were captured by MGNPs and combined with SERS tags, forming a "sandwich" composite structure for bacterial detection.

Results

AuNSs, with a core size of 65 nm, exhibited excellent storage stability (RSD=5.6%) and demonstrated superior SERS enhancement compared to colloidal gold nanoparticles. Efficient binding of S. aureus and P. aeruginosa to MGNPs resulted in capture efficiencies of 89.13% and 85.31%, respectively. Under optimized conditions, the developed assay achieved a limit of detection (LOD) of 7 CFU/mL for S. aureus and 5 CFU/mL for P. aeruginosa. The bacterial concentration (10-106 CFU/mL) showed a strong linear correlation with the SERS intensity at 1331 cm-1. Additionally, high recoveries (84.8% - 118.0%) and low RSD (6.21% - 11.42%) were observed in spiked human urine samples.

Conclusion

This study introduces a simple and innovative magnetically-assisted SERS biosensor for the sensitive and quantitative detection of S. aureus or P. aeruginosa, utilizing WGA and antibodies. The developed biosensor enhances the capabilities of the "sandwich" type SERS biosensor, offering a novel and effective platform for accurate and timely clinical diagnosis of bacterial infections.

MXene/zinc ion embedded agar/sodium alginate hydrogel for rapid and efficient sterilization with photothermal and chemical synergetic therapy

Bacterial infections can significantly impair wound healing. Therefore, it is essential to develop wound dressings with high antimicrobial activity. Hydrogels are often used as wound dressings due to their excellent physicochemical properties. Herein, by cross linking sodium alginate (SA), agar (AG) with Ti3C2Tx MXene and Zinc ions (Zn2+), a biosafe composite hydrogel (MSG-Zn2+) was developed for fast and efficient sterilization treatment. The excellent photothermal properties of Ti3C2Tx MXene and the chemical antimicrobial activity of Zn2+ enable synergistic photothermal therapy (PTT)/chemical therapy in NIR biowindow with reduced power density and improved antimicrobial efficiency. More importantly, the incorporation of Zn2+ can enhance the effective contact between the hydrogel and bacteria, benefiting both photothermal and chemical antibacteria. In vitro antibacterial experiments showed that MSG-Zn2+ has a broad-spectrum antibacterial effect against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). Cellular experiments showed that the hydrogel had excellent biocompatibility and the released Zn2+ stimulated cell migration. In addition, the prepared MSG-Zn2+ hydrogel has other advantages such as hydrophilic, high swelling, simple and low cost preparation, which meets the requirements of an economical wound dressing. This proposed work shows that this composite hydrogel MSG-Zn2+ has great potential for practical antimicrobial wound dressing applications.

Construction of "Coral" SERS sensor for ultrasensitive and rapid detection of harmful component macrophage migration inhibitory factor in Platelet-rich Plasma

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory factor produced by residual red blood cell lysis, which can significantly influence the curative effect of Platelet-rich plasma (PRP) therapy used for osteoarthritis (OA) treatment. In this study, we proposed a novel approach for detecting the concentration of MIF in PRP using a dopamine-coated antibody-Au (core)-Ag (shell)-SERS sensor, which enables ultrasensitive and rapid detection of MIF. The best experimental conditions have a detection limit of only 90.05 pg/mL and a good linear relationship between 1-5000 ng/mL. In 40 PRP samples collected from actual clinical patients, we detected MIF concentrations ranging from 2.0-3.6 ng/mL. This indicated that the Coral SERS sensor not only allows for results highly consistent with the traditional ELISA method, but also costs less ($0.40-$0.70), needs shorter testing time (integration time is only 10s), and consumes less PRP that can greatly improve the sample quality and maximize the curative effect in clinical applications for OA treatment with PRP.

In Situ Tyrosinase Monitoring by Wearable Microneedle Patch toward Clinical Melanoma Screening

Despite the potential indicating role of tyrosinase (TYR) in cutaneous melanoma, how to capture the real changes of TYR in suspicious skin remains a major challenge. Unlike the traditional human serum test, this study reports a sensing platform that incorporates a wearable microneedle (MN) patch and trimetallic Au@Ag-Pt nanoparticles (NPs) for surface-enhanced Raman scattering (SERS) and colorimetric dual-mode detecting TYR in human skin in situ toward potential melanoma screening. In the presence of TYR, catechol immobilized on MN is preferentially oxidized to benzoquinone, which competitively impedes the interaction of MN and Au@Ag-Pt NPs, triggering the SERS-colorimetric signal reciprocal switch. Using a B16F10 mouse melanoma model, our platform is capable of noninvasively piercing the skin surface and detecting TYR levels before and during anti-PD-1 antibody treatment, which would be highly informative for prognostic judgment and illness monitoring of melanoma. Through in situ sensing for capturing the metabolic changes of TYR in advance, this platform was successfully applied to discriminate the melanoma subjects from skin moles and normal ones (p < 0.001), as well as screen potential melanoma from lactate dehydrogenase (LDH)-negative patients. Melanoma growth and prognosis can still be monitored through recording the continuous change of TYR levels. More importantly, the well-defined flexible and stretchable characteristics of the MN patch allow robustly adhering to the skin without inducing chemical or physical irritation. We believe this platform integrating MN-based in situ sensing, TYR responsiveness, and SERS/colorimetric dual-readout strategy will have high clinical importance in early diagnosis and monitoring of cutaneous melanoma.

Bioinspired hot-spot engineering strategy towards ultrasensitive SERS sandwich biosensor for bacterial detection

Surface-enhanced Raman spectroscopy (SERS) sandwich biosensors have received tremendous attention in early diagnosis of bacterial infections. However, efficiently engineering nanoscale plasmonic hots pots (HS) towards ultrasensitive SERS detection still remains challenging. Herein, we propose a bioinspired synergistic HS engineering strategy to construct ultrasensitive SERS sandwich bacterial sensor (named USSB), by coupling bioinspired signal module and plasmonic enrichment module to synergistically boost the number and intensity of HS. The bioinspired signal module is based on dendritic mesoporous silica nanocarrier (DMSN) loaded with plasmonic nanoparticles and SERS tag, while magnetic Fe3O4 nanoparticles coated with Au shell are employed in plasmonic enrichment module. We demonstrate that DMSN effectively shrank nanogaps between plasmonic nanoparticles to improve HS intensity. Meanwhile, plasmonic enrichment module contributed to plenty of additional HS inside and outside individual "sandwich". Ascribing to the boosted number and intensity of HS, the constructed USSB sensor exhibits ultrahigh detection sensitivity (7 CFU/mL) and selectivity towards model pathogenic bacteria of Staphylococcus aureus. Remarkably, the USSB sensor enables fast and accurate bacterial detection in real blood samples of septic mice, achieving early diagnosis of bacterial sepsis. The proposed bioinspired synergistic HS engineering strategy opens up a new direction for constructing ultrasensitive SERS sandwich biosensors, and may promote their advancing applications in the early diagnosis and prognosis of devastating diseases.

Urchin-Shaped Au-Ag@Pt Sensor Integrated Lateral Flow Immunoassay for Multimodal Detection and Specific Discrimination of Clinical Multiple Bacterial Infections

A new lateral flow immunoassay strip (LFIA) combining sensitive detection and identification of multiple bacteria remains a huge challenge. In this study, we first developed multifunctional urchin-shaped Au-Ag@Pt nanoparticles (UAA@P NPs) with a unique combination of colorimetric-SERS-photothermal-catalytic (CM/SERS/PT/CL) properties and integrated them with LFIA for multiplexed detection and specific discrimination of pathogenic bacteria in blood samples. Unlike the conventional LFIA that relied on antibody (Ab), this novel LFIA introduced 4-mercaptophenylboronic acid (4-MPBA) as an ideal Ab replacer that was functionalized on UAA@P NPs (UAA@P/M NPs) with outstanding binding and enrichment capacities toward bacteria. Taking Staphylococcus aureus (S. aureus) as model bacteria, the limit of detection (LOD) was 3 CFU/mL for SERS-LFIA, 27 CFU/mL for PT-LFIA, and 18 CFU/mL for CL-LFIA, three of which were over 330-fold, 37-fold, and 55-fold more sensitive than ordinary visual CM-LFIA, respectively. Besides, this SERS-LFIA is capable of identifying three types of bacterial spiked blood samples (E. coli, S. aureus, and P. aeruginosa) effectively according to specific bacterial Raman "fingerprints" by partial least-squares-discriminant analysis (PLS-DA). More importantly, this LFIA was successfully applied to blood samples with satisfactory recoveries from 90.3% to 108.8% and capable of identifying the infected patients (N = 4) from healthy subjects (N = 2) with great accuracy. Overall, the multimodal LFIA incorporates bacteria discrimination and quantitative detection, offering an avenue for early warning and diagnosis of bacterial infection.

Colorimetric determination and recycling of gold(III) ions using label-free plasmonic H0.3MoO3 nanoparticles

A low-cost and environment-friendly sensor was developed for visual determination of gold ions (Au³⁺) by using label-free hydrogen doped molybdenum oxide (H_0.3MoO₃) nanoparticles as ratio probes. According to the characterization results of transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectra, Au³⁺ is easily reduced to red Au nanoparticles (AuNPs) by blue H_0.3MoO₃ nanoparticles. The color change of the solution depends on the concentration of Au³⁺, which makes it possible to detect Au³⁺ visually. Under optimal experimental conditions of pH 4.6, H_0.3MoO₃ nanoparticles concentration of 0.075 mg·mL^-1, and reaction time of 7 min, the sensor offers a satisfactory determination range from 0.5 to 70 μM and a good determination limit of 0.45 μM for Au³⁺. The concentration of Au³⁺ as low as 10 μM can be directly distinguished through the naked eye. Additionally, the colorimetric probe has also been proved applicable in environmental water samples. More importantly, the resulting AuNPs have good stability and oxidase-like activity, which may be directly used in sensing, catalysis, energy, and other fields.

Well-Ordered Au Nanoarray for Sensitive and Reproducible Detection of Hepatocellular Carcinoma-Associated miRNA via CHA-Assisted SERS/Fluorescence Dual-Mode Sensing

Ultra-sensitive detection of cancer-related biomarkers in serum is of great significance for early diagnosis, treatment, prognosis, and staging of cancer. In this work, we proposed a surface-enhanced Raman scattering and fluorescence (SERS/FL) dual-mode biosensor for hepatocellular carcinoma (HCC)-related miRNA (miR-224) detection using the composition of well-arranged Au nanoarrays (Au NAs) substrate coupled with the target-catalyzed hairpin assembly (CHA) strategy. The hot spots densely and uniformly distributed on the Au array offers considerably enhanced and reproducible SERS signals, along with their wide and open surface to facilitate miR-224 adsorption. By this sensing strategy, the target miR-224 can be detected in a wide linear range (1 fM to 1 nM) with a limit of detection of 0.34 fM in the SERS mode and 0.39 fM in the FL mode. Meanwhile, this biosensor with exceptional specificity and anti-interference ability can discriminate target miR-224 from other interference miRNAs. Practical analysis of human blood samples also demonstrated considerable reliability and repeatability of our developed strategy. Furthermore, this biosensor can distinguish HCC cancer subjects from normal ones and monitor HCC patients before and after hepatectomy as well as guide the distinct Barcelona clinic liver cancer (BCLC) stages. Overall, benefiting from a well-arranged Au nanoarray, CHA amplification strategy, and SERS/metal enhanced fluorescence effect, this established biosensor opens new avenues for the early prediction, warning, monitoring, and staging of HCC.

Real-time SERS monitoring anticancer drug release along with SERS/MR imaging for pH-sensitive chemo-phototherapy

In situ and real-time monitoring of responsive drug release is critical for the assessment of pharmacodynamics in chemotherapy. In this study, a novel pH-responsive nanosystem is proposed for real-time monitoring of drug release and chemo-phototherapy by surface-enhanced Raman spectroscopy (SERS). The Fe3O4@Au@Ag nanoparticles (NPs) deposited graphene oxide (GO) nanocomposites with a high SERS activity and stability are synthesized and labeled with a Raman reporter 4-mercaptophenylboronic acid (4-MPBA) to form SERS probes (GO-Fe3O4@Au@Ag-MPBA). Furthermore, doxorubicin (DOX) is attached to SERS probes through a pH-responsive linker boronic ester (GO-Fe3O4@Au@Ag-MPBA-DOX), accompanying the 4-MPBA signal change in SERS. After the entry into tumor, the breakage of boronic ester in the acidic environment gives rise to the release of DOX and the recovery of 4-MPBA SERS signal. Thus, the DOX dynamic release can be monitored by the real-time changes of 4-MPBA SERS spectra. Additionally, the strong T2 magnetic resonance (MR) signal and NIR photothermal transduction efficiency of the nanocomposites make it available for MR imaging and photothermal therapy (PTT). Altogether, this GO-Fe3O4@Au@Ag-MPBA-DOX can simultaneously fulfill the synergistic combination of cancer cell targeting, pH-sensitive drug release, SERS-traceable detection and MR imaging, endowing it great potential for SERS/MR imaging-guided efficient chemo-phototherapy on cancer treatment.

Integration of three non-interfering SERS probes combined with ConA-functionalized magnetic nanoparticles for extraction and detection of multiple foodborne pathogens

A sandwich-structured SERS biosensor has been constructed for simultaneous detection of multiple pathogenic bacteria, consisting of non-interfering SERS probes for bacterial labeling and ConA-functionalizd magnetic nanoparticles for bacteria extraction. A the preparation method of PP3 SERS probe with high Raman activity is reported for the first time. Since the PP3 SERS probe has a very strong Raman peak at 2081 cm^-1 in the "Raman silent region," the mixed SERS probe formed with MP1 and DP2 can meet the needs of multiple foodborne pathogen detection. Significantly, S. aureus, E. coli, and P. aeruginosa can be successfully extracted upon external magnetic field, and the limit of detection (LOD) is 1 CFU‧mL^-1, lower than that of the congeneric detectors. This work paves a new way for the construction of a novel detector and absorbent for different bacteria in complex samples by using SERS probe.

Engineering a SERS Sensing Nanoplatform with Self-Sterilization for Undifferentiated and Rapid Detection of Bacteria

The development of a convenient, sensitive, rapid and self-sterilizing biosensor for microbial detection is important for the prevention and control of foodborne diseases. Herein, we designed a surface-enhanced Raman scattering (SERS) sensing nanoplatform based on a capture-enrichment-enhancement strategy to detect bacteria. The gold-Azo@silver-cetyltrimethylammonium bromide (Au-Azo@Ag-CTAB) SERS nanotags were obtained by optimizing the synthesis process conditions. The results showed that the modification of CTAB enabled the nanotags to bind to different bacteria electrostatically. This SERS sensing nanoplatform was demonstrated to be fast (15 min), accurate and sensitive (limit of detection (LOD): 300 and 400 CFU/mL for E. coli and S. aureus, respectively). Of note, the excellent endogenous antibacterial activity of CTAB allowed the complete inactivation of bacteria after the assay process, thus effectively avoiding secondary contamination.