Salmonella typhimurium detector based on the intrinsic peroxidase-like activity and photothermal effect of MoS2

Overview of the Design and Application of Photothermal Immunoassays

Developing powerful immunoassays for sensitive and real-time detection of targets has always been a challenging task. Due to their advantages of direct readout, controllable sensing, and low background interference, photothermal immunoassays have become a type of new technology that can be used for various applications such as disease diagnosis, environmental monitoring, and food safety. By modification with antibodies, photothermal materials can induce temperature changes by converting light energy into heat, thereby reporting specific target recognition events. This article reviews the design and application of photothermal immunoassays based on different photothermal materials, including noble metal nanomaterials, carbon-based nanomaterials, two-dimensional nanomaterials, metal oxide and sulfide nanomaterials, Prussian blue nanoparticles, small organic molecules, polymers, etc. It pays special attention to the role of photothermal materials and the working principle of various immunoassays. Additionally, the challenges and prospects for future development of photothermal immunoassays are briefly discussed.

Application of photothermal effects of nanomaterials in food safety detection

Numerous nanomaterials endowed with outstanding light harvesting and photothermal conversion abilities have been extensively applied in various fields, such as photothermal diagnosis and therapy, trace substance detection, and optical imaging. Although photothermal detection methods have been established utilizing the photothermal effect of nanomaterials in recent years, there is a scarcity of reviews regarding their application in food safety detection. Herein, the recent advancements in the photothermal conversion mechanism, photothermal conversion efficiency calculation, and preparation method of photothermal nanomaterials were reviewed. In particular, the application of photothermal nanomaterials in various food hazard analyses and the newly established photothermal detection methods were comprehensively discussed. Moreover, the development and promising future trends of photothermal nanomaterial-based detection methods were discussed, which provide a reference for researchers to propose more effective, sensitive, and accurate detection methods.

A gas-driven capillary based on the synergy of the catalytic and photothermal effect of PB@Au for Salmonella typhimurium detection

Rapid detection method for Salmonella typhimurium is vital to prevent the spread of food-borne diseases. In this work, a gas-driven capillary detection method was established to achieve sensitive and rapid detection of Salmonella typhimurium using the catalytic and photothermal synergy of Prussian blue-nanogold (PB@Au) nanomaterials. The immuno-PB@Au probe attached to the capillary by specific identification of target bacteria catalyzed the H2O2 under laser irradiation, driving the H2O2 liquid column to move (ΔL) by producing gas, and achieving the quantitative detection of Salmonella typhimurium. After detailed optimization of the critical performance parameters of the gas-driven capillary assay, the limit of detection (LOD) after laser irradiation and being catalyzed by PB@Au was calculated to be 37 CFU mL-1 through the determination of different concentrations of target bacteria. Furthermore, the detection performances of the gas-driven capillary method were evaluated in detail, and the recoveries ranging from 92.9 ± 4.7 % to 107.7 ± 4.1 % were achieved using the spiked actual samples with complex matrices, indicating that the established rapid assay can offer promising strategies for the monitoring and controlling of food-borne pathogenic bacteria.

Optically active two-dimensional MoS2-based nanohybrids for various biosensing applications: A comprehensive review

Following the discovery of graphene, there has been a surge in exploring other two-dimensional (2D) nanocrystals, including MoS2. Over the past few decades, MoS2-based nanocrystals have shown great potential applications in biosensing, owing to their excellent physico-chemical properties. Unlike graphene, MoS2 shows layer-dependent finite band gaps (∼1.8 eV for a single layer and ∼1.2 for bulk) and relatively strong interaction with the electromagnetic spectrum. The tunability of the size, shape, and intrinsic properties, such as high optical absorption, electron mobility, mechanical strength and large surface area, of MoS2 nanocrystals, make them excellent alternative probe materials for preparing optical, photothermal, and electrical bio/immunosensors. In this review, we will provide insights into the rapid evolutions in bio/immunosensing applications based on MoS2 and its nanohybrids. We emphasized the various synthesis, characterization, and functionalization routes of 2D MoS2 nanosheets/nanoflakes. Finally, we discussed various fabrication techniques and the critical parameters, including the limit of detection (LOD), linear detection range, and sensitivity of the biosensors. In addition, the role of MoS2 in enhancing the performance of biosensors, the limitations associated with current biosensing technologies, future challenges, and clinical implications are addressed. The advantages/disadvantages of each biosensor technique are also summarized. Collectively, we believe that this review will encourage resolute researchers to follow up further with the state-of-the-art MoS2-based biosensing technology.

Rapid detection of Salmonella in food matrices by photonic PCR based on the photothermal effect of Fe3O4

Salmonella causes most deaths from diarrheal disease worldwide. Therefore, Salmonella must be accurately and quickly detected, even in complex food matrices, which is difficult to achieve using conventional culture methods. Here we propose a novel photonic polymerase chain reaction (PCR) method based on ferroferric oxide (Fe3O4) for the detection of Salmonella typhimurium in complex samples. Owing to the great photothermal conversion performance of Fe3O4, rapid thermal cycling could be accomplished. Our optimized photonic PCR system specifically detected Salmonella typhimurium in complex food matrices within 50 min. Quantitative data showed a limit of detection up to 102 CFU/mL in food samples. This method is suitable for the detection of all pathogenic microorganisms and is universal.

Smartphone-Based Photothermal Lateral Flow Immunoassay Using Rhenium Diselenide Nanosheet

Developing a rapid antibody-based detection method is of great importance for preventing and controlling the spread of coronavirus disease 2019 (COVID-19). Among the antibody-based methods for point-of-care (POC) detection, lateral flow immunoassay (LFIA) is the most widely used. However, LFIA still has the disadvantage of low sensitivity. In this work, an ReSe2 nanosheet with a thickness of 10-20 nm was prepared by liquid exfoliation and applied as the label in a photothermal LFIA due to its high photothermal conversion efficiency and high photothermal stability. An integrated detection device was introduced for rapid, on-site, and highly sensitive assay of the human antisevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike (S) protein IgG antibodies. The device mainly included a rhenium diselenide (ReSe2) nanosheet-based photothermal LFIA, a portable laser, and a smartphone with a portable thermal imager, which was used to record and analyze the thermal signal of the LFIA test zone. The human anti-SARS-COV-2 S protein IgG antibodies in buffer solution can be detected in a portable box within 10 min, with a thermal signal detection limit of 0.86 ng mL-1, which was 108-fold lower than that of the colorimetric signal. The integrated device can detect values as low as 2.76 ng mL-1 of the human anti-SARS-COV-2 S protein IgG antibodies in 50% serum. The integrated device showed great potential for rapid and home self-testing diagnosis of COVID-19.

Salmonella typhimurium strip based on the photothermal effect and catalytic color overlap of PB@Au nanocomposite

This work reports a sensitive and accurate multimode detection method to detect Salmonella typhimurium using inherent color, photothermal and catalytic properties of Prussian blue@gold nanoparticles (PB@Au). The inherent color of PB@Au can realize direct visual detection while the temperature increase (ΔT) of it can realize sensitive and quantitative photothermal detection. Moreover, catalytic coloration detection is applied to further amplify detection signal. The risk limit, prevention and control of Salmonella typhimurium can be more intuitively displayed through catalytic color overlap degree between PB@Au and catalytic product. The sensitivity of method is improved through photothermal and catalytic coloration detection (10¹ CFU·mL^-1) compared with direct visual detection (10² CFU·mL^-1). The multimode detection improves the accuracy of method, and exhibits good repeatability, acceptable selectivity and stability. This method is also successfully applied in real samples, displaying its good practical applicability.

Rapid qualitative and quantitative detection of Salmonella typhimurium using a single-step dual photometric/fluorometric assay

A dual-signal photometric/fluorometric assay was established for rapid, qualitative, and quantitative detection of Salmonella typhimurium (S. typhimurium). This method was composed of two parts: (1) a single-step photometric (SSC) assay containing gold nanoparticles (AuNPs), poly-diallyldimethylammonium chloride (PDDA), and S. typhimurium-specific aptamer, and (2) a fluorescence (FL) assay containing carboxyl-modified CdSe/ZnS quantum dots (QDs-_COOH). Users just need to drop samples contaminated with S. typhimurium into SSC assay; the apparent color change from red to blue can be observed in a short time (20 min). A smartphone app was developed to read the semiquantitative result. By subsequently adding one drop of FL assay into the reaction mixture, the generated fluorescence intensity reflected the concentration of S. typhimurium. The naked eye limit of detection (LOD) and fluorescent LOD were 10³ cfu/mL and 10 cfu/mL, respectively. This method exhibited good selectivity. The reliability and practicability were verified by testing contaminated food, drinking water, and pets' urine.

Photothermal card reader assay using the commercial colloidal gold test strip for the rapid quantitative detection of food hazards

The simple and rapid commercial colloidal gold test strip can only be used for qualitative or semi-quantitative detection, accompanied by weak detectability and false negative experimental results. Herein, a photothermal test strip assay which combined test strip with a portable photothermal card reader was established to achieve quantitative detection with excellent detectability. According to the photothermal effect produced by gold nanoparticles (GNPs) captured on the test line, the signal could be recorded by the reader. Thirteen food hazards including veterinary drug residues and pesticide residues were tested; the photothermal detectability in actual samples were about 23 (methyl parathion), 7 (enrofloxacin), 6 (sarafloxacin), 8 (sulfadiazine), 12 (sulfamethazine), 7 (paraquat), 6 (malachite green), 11 (amantadine), 13 (nitrofurazone), 6 (diethylstilbestrol), 12 (estriol), 21 (estrone), and 26 (17β-estradiol) times better than the visual detectability. Our results demonstrated that the photothermal test strip assay could be used for sensitive, rapid, and quantitative detection of residues of food hazards.

A rapid and ultrasensitive dual detection platform based on Cas12a for simultaneous detection of virulence and resistance genes of drug-resistant Salmonella

Accurate, sensitive, and rapid detection of Salmonella and determination of whether it carries drug resistance genes plays an important role in guiding the clinical medication of salmonellosis and laying a foundation for studying the mechanism of drug resistance transmission of Salmonella. Here, a novel nontransferable, ultrasensitive dual detection platform (Cas12a-Ddp) was developed. The round cap allowed for temporary storage of more Cas12a detection solution than flat cap, enabling one-pot assays and reducing aerosol contamination. The results were read out in dual mode by the microplate reader and UV visualization to achieve sensitive dual-target detection of the virulence genes and drug resistance genes of Salmonella simultaneously, with the possibility of onsite detection. Cas12a-Ddp was combined with multiple polymerase chain reactions and recombinase polymerase amplifications successively. An ultrasensitive dual detection limit of 1 CFU/mL was obtained without any cross-reaction within 40 min. This was an improvement of 1-2 orders of magnitude over the existing methods. Cas12a-Ddp overcame the influence of proteins and fat in liquid matrix foods. It was used for the detection of drug-resistant Salmonella in milk and skim milk powder, also with the dual detection limit of 1 CFU/mL and spiked recovery of 68.58%-158.49%. It was also used for the analysis of Salmonella resistance rate analysis. The Cas12a-Ddp provided a reliable, fast, sensitive, and practical multi-CRISPR detection platform.

Overview of Rapid Detection Methods for Salmonella in Foods: Progress and Challenges

Salmonella contamination in food production and processing is a serious threat to consumer health. More and more rapid detection methods have been proposed to compensate for the inefficiency of traditional bacterial cultures to suppress the high prevalence of Salmonella more efficiently. The contamination of Salmonella in foods can be identified by recognition elements and screened using rapid detection methods with different measurable signals (optical, electrical, etc.). Therefore, the different signal transduction mechanisms and Salmonella recognition elements are the key of the sensitivity, accuracy and specificity for the rapid detection methods. In this review, the bioreceptors for Salmonella were firstly summarized and described, then the current promising Salmonella rapid detection methods in foodstuffs with different signal transduction were objectively summarized and evaluated. Moreover, the challenges faced by these methods in practical monitoring and the development prospect were also emphasized to shed light on a new perspective for the Salmonella rapid detection methods applications.