Simultaneous detection of Staphylococcus aureus and Salmonella typhimurium using multicolor time-resolved fluorescence nanoparticles as labels

Shining light on carbon dots: Toward enhanced antibacterial activity for biofilm disruption

In spite of tremendous efforts dedicated to addressing bacterial infections and biofilm formation, the post-antibiotic ear continues to witness a gap between the established materials and an easily accessible yet biocompatible antibacterial reagent. Here we show carbon dots (CDs) synthesized via a single hydrothermal process can afford promising antibacterial activity that can be further enhanced by exposure to light. By using citric acid and polyethyleneimine as the precursors, the photoluminescence CDs can be produced within a one-pot, one-step hydrothermal reaction in only 2 h. The CDs demonstrate robust antibacterial properties against both Gram-positive and Gram-negative bacteria and, notably, a considerable enhancement of antibacterial effect can be observed upon photo-irradiation. Mechanistic insights reveal that the CDs generate singlet oxygen (1O2) when exposed to light, leading to an augmented reactive oxygen species level. The approach for disruption of biofilms and inhibition of biofilm formation by using the CDs has also been established. Our findings present a potential solution to combat antibacterial resistance and offer a path to reduce dependence on traditional antibiotics.

Advanced diagnostic methods for identification of bacterial foodborne pathogens: contemporary and upcoming challenges

It is a public health imperative to have safe food and water across the population. Foodborne infections are one of the primary causes of sickness and mortality in both developed and developing countries. An estimated 100 million foodborne diseases and 120 000 foodborne illness-related fatalities occur each year in India. Several factors affect foodborne illness, such as improper farming methods, poor sanitary and hygienic conditions at all levels of the food supply chain, the lack of preventative measures in the food processing industry, the misuse of food additives, as well as improper storage and handling. In addition, chemical and microbiological combinations also play a key role in disease development. But recent disease outbreaks indicated that microbial pathogens played a major role in the development of foodborne diseases. Therefore, prompt, rapid, and accurate detection of high-risk food pathogens is extremely vital to warrant the safety of the food items. Conventional approaches for identifying foodborne pathogens are labor-intensive and cumbersome. As a result, a range of technologies for the rapid detection of foodborne bacterial pathogens have been developed. Presently, many methods are available for the instantaneous detection, identification, and monitoring of foodborne pathogens, such as nucleic acid-based methods, biosensor-based methods, and immunological-based methods. The goal of this review is to provide a complete evaluation of several existing and emerging strategies for detecting food-borne pathogens. Furthermore, this review outlines innovative methodologies and their uses in food testing, along with their existing limits and future possibilities in the detection of live pathogens in food.

A Dual-Mode Method Based on Aptamer Recognition and Time-Resolved Fluorescence Resonance Energy Transfer for Histamine Detection in Fish

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2-1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness.

Multiplex optical bioassays for food safety analysis: Toward on-site detection

Food safety analysis plays a significant role in controlling food contamination and supervision. In recent years, multiplex optical bioassays (MOBAs) have been widely applied to analyze multiple hazards due to their efficiency and low cost. However, due to the challenges such as multiplexing capacity, poor sensitivity, and bulky instrumentation, the further application of traditional MOBAs in food screening has been limited. In this review, effective strategies regarding food safety MOBAs are summarized, such as spatial-resolution modes performed in multi-T lines/dots strips or arrays of strip/microplate/microfluidic chip/SPR chip and signal-resolution modes employing distinguishable colorimetric/luminescence/fluorescence/surface plasma resonance/surface-enhanced Raman spectrum as signal tags. Following this, new trends on how to design engineered sensor architecture and exploit distinguishable signal reporters, how to improve both multiplexing capacity and sensitivity, and how to integrate these formats into smartphones so as to be mobile are summarized systematically. Typically, in the case of enhancing multiplexing capacity and detection throughput, microfluidic array chips with multichannel architecture would be a favorable approach to overcome the spatial and physical limitations of immunochromatographic assay (ICA) test strips. Moreover, noble metal nanoparticles and single-excitation, multiple-emission luminescence nanomaterials hold great potential in developing ultrasensitive MOBAs. Finally, the exploitation of innovative multiplexing strategy hybridized with powerful and widely available smartphones opens new perspectives to MOBAs. In future, the MOBAs should be more sensitive, have higher multiplexing capacity, and easier instrumentation.

Rapid and selective detection of Bacillus cereus in food using cDNA-based up-conversion fluorescence spectrum copy and aptamer modified magnetic separation

A sensitive luminescent bioassay for the detection of Bacillus cereus (B. cereus), a common bacterium, harmful to human health, was established based on up-conversion fluorescence and magnetic separation technology. Herein, aptamers (Apt) are modified on the surface of magnetic nanoparticles (MNPs) to form Apt-MNPs capture probes. The aptamer complementary strands (cDNA) are connected to upconversion nanoparticles (UCNPs) to form UCNPs-cDNA signal probes. In the absence of analyte, the UCNPs-cDNA-Apt-MNPs complex will be formed due to the specific binding between the aptamer and the complementary strand. In the presence of B. cereus, the amount of free UCNPs-cDNA increased in the system, which ultimately increased the fluorescence intensity of the solution. Hence, when the UCNPs-cDNA-Apt-MNPs system was excited by a 980 nm near-infrared light, a decrease in the fluorescence of the complex was observed at 548 nm due to the detachment of UCNPs-cDNA. Therefore, based on this principle, the calibration curve is constructed between the concentration of the analyte (B. cereus) and the fluorescence intensity. The results show that the method has a good quantitative ability for B. cereus in the range of 49-49 × 10⁶ cfu/mL under the optimal conditions with a detection limit of 22 cfu/mL. Moreover, the proposed detection method also exhibits a high degree of specificity. The spiked recovery rate of the actual sample was in the range of 90.54%-111.28%, with good relative standard deviation values (2.12%-3.13%), indicating that the method has good reproducibility and stability. This study demonstrates that the constructed method can be used successfully for the rapid detection of B. cereus in food.

Fluorescence resonance energy transfer-based aptasensor for sensitive detection of kanamycin in food

Kanamycin (KAN) is widely used in animal husbandry to treat bacterial infections. However, excessive KAN may cause residues and be transmitted to humans and the environment, causing serious adverse effects on humans. Herein, a simple fluorescence resonance energy transfer (FRET)-based aptasensor has been developed for sensitive detection of KAN in food. In the absence of KAN, UCNPs-aptamer hybridized with BHQ3-cDNA and quenched fluorescence was observed due to the FRET effect between BHQ3 and UCNPs. In the presence of KAN, double strands separated and the fluorescence intensity was recovered. Additionally, a linear relation (R² = 0.9926) was found in the range of 0.05-50 μM and the recovered fluorescence intensity at 654 nm with a detection limit of 18.9 nM. The method was verified by standard recovery method and HPLC with satisfactory recovery rate (87.0-109.6%) and accuracy (P > 0.05). These results showed the proposed method could be successfully applied to detect KAN in food samples.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

Application of Multiplexed Aptasensors in Food Contaminants Detection

The existence of contaminants in food poses a serious threat to human health. In recent years, aptamer sensors (aptasensors) have been developed rapidly for the detection of food contaminants because of their high specificity, design flexibility, and high efficiency. However, the development of high-throughput, highly sensitive, on-site, and cost-effective methods for simultaneous detection of food contaminants is still restricted due to multiple signal overlap or mutual interference and cross-reaction between different analytes with similar molecular structures. To overcome these problems, this Review summarizes some effective strategies from the articles published in recent years about multiplexed aptasensors for the simultaneous detection of food contaminants. This work focuses on the application of multiplexed aptasensors to simultaneously detect antibiotics, pathogens, and mycotoxins in food. These aptasensors mainly contain fluorescent aptasensors, electrochemical aptasensors, surface-enhanced Raman scattering-based aptasensors, microfluidic chip aptasensors, and paper-based multiplexed aptasensors. In addition, this Review also covers the application of nucleic acid cycle amplification and nanomaterial amplification strategies to improve the detection sensitivity. Finally, the limitations and challenges in the design of multiplexed aptasensor are also taken into account.

Colorimetric method for Salmonella spp. detection based on peroxidase-like activity of Cu(II)-rGO nanoparticles and PCR

Development of a rapid and sensitive method for Salmonella spp. detection is of great importance for ensuring food product safety due to its low infective dose. In this study, a colorimetric method based on the peroxidase-like activity of Cu(II)-modified reduced graphene oxide nanoparticles (Cu²⁺-rGO NPs) and PCR was successfully developed to detect Salmonella spp. in milk. Under optimal conditions, the developed colorimetric method exhibited high sensitivity and strong specificity for Salmonella spp. detection. The limit of detection was 0.51 CFU/mL with a linear range from 1.93 × 10¹ to 1.93 × 10⁵ CFU/mL. A specificity study demonstrated that this method can specifically distinguish Salmonella typhimurium and Salmonella enteritidis from other foodborne pathogens. The application of the proposed method for milk sample detection was also validated, and the recovery rates of S. typhimurium in spiked milk sample ranged from 102.84% to 112.25%. This colorimetric sensor exhibits enormous potential for highly sensitive detection of bacteria in milk sample.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

A time-resolved luminescence aptasensor of ofloxacin based on rolling circle amplification and magnetic separation

A novel sensitive, competitive, and time-resolved luminescence sensor for the detection of ofloxacin (OFL) was developed in this study. The sensor used OFL-specific aptamer as a recognition molecule and rolling circle amplification (RCA) as a signal amplification tool. In this way, the time-resolved luminescence can not only avoid background noise from sample, but also provide robust luminescence for detection. Besides, the separation and enrichment of target veterinary drug can be conducted assisted by magnetic treatment. Under optimal conditions, the logarithmic correlation between the concentration of OFL and the luminescence intensity was found to be linear in the range of 5 × 10^-11-5 × 10^-8 mol L^-1 (R² = 0.9988), with a detection limit (LOD) of 32.1 pmol L^-1. Furthermore, this method was applied to the determination of OFL in chicken and pork samples, exhibiting good recovery (72.5-100%) and repeatability (RSD < 10.0%). These results confirm that this novel established method has good application potential for the detection of OFL in food samples.

Construction of Time-Resolved Luminescence Nanoprobe and Its Application in As(III) Detection

As(III) is a toxic heavy metal which causes serious health problems. Therefore, the development of highly sensitive sensors for As(III) detection is of great significance. Herein, a turn-on luminescence resonance energy transfer (LRET) method based on luminous nanorods was designed for As(III) detection. Biotin-labelled As(III) aptamers were tagged to avidin functionalized luminous nanorods as energy donors, while graphene oxide (GO) acted as the energy acceptor. The adsorption of single-stranded DNA on graphene oxide resulted in the efficient quenching of the luminescence of the nanorods through the LRET process. In the presence of As(III), aptamers bonded to As(III) preferentially and resulted in the formation of aptamer-As(III) complexes. The aptamer-As(III) complexes were rubbed off from the GO surface due to their conformational change, which led to the recovery of the luminescence of the nanorods. A good linear relationship between the luminescence intensity and concentration of As(III) was obtained in the range from 1 to 50 ng·mL⁻¹, with a detection limit of 0.5 ng·mL⁻¹. Furthermore, the developed sensors showed good specificity towards As(III) and proved capable of detecting As(III) in the environment and food samples. The proposed time-resolved sensors provide a promising sensing strategy for the rapid and sensitive detection of As(III).

Detection of Salmonella in Food Matrices, from Conventional Methods to Recent Aptamer-Sensing Technologies

Rapid detection of the foodborne pathogen Salmonella in food processing is of crucial importance to prevent food outbreaks and to ensure consumer safety. Detection and quantification of Salmonella species in food samples is routinely performed using conventional culture-based techniques, which are labor intensive, involve well-trained personnel, and are unsuitable for on-site and high-throughput analysis. To overcome these drawbacks, many research teams have developed alternative methods like biosensors, and more particularly aptasensors, were a nucleic acid is used as biorecognition element. The increasing interest in these devices is related to their high specificity, convenience, and relative rapid response. This review aims to present the advances made in these last years in the development of biosensors for the detection and the quantification of Salmonella, highlighting applications on meat from the chicken food chain.

Research advances of DNA aptasensors for foodborne pathogen detection

Aptamers, referring to single-stranded DNA or RNA molecules can specifically recognize and bind to their targets. Based on their excellent specificity, sensitivity, high affinity, and simplicity of modification, aptamers offer great potential for pathogen detection and biomolecular screening. This article reviews aptamer screening technologies and aptamer application technologies, including gold-nanoparticle lateral flow assays, fluorescence assays, electrochemical assays, colorimetric assays, and surface-enhanced Raman assays, in the detection of foodborne pathogens. Although notable progress (more rapid, sensitive, and accurate) has been achieved in the field, challenges and drawbacks in their applications still remain to be overcome.

Functional chimera aptamer and molecular beacon based fluorescent detection of Staphylococcus aureus with strand displacement-target recycling amplification

A fluorescent detection of Staphylococcus aureus (S. aureus) is established based on a finely designed functional chimera sequence, a molecular beacon (MB), and strand displacement target recycling. The chimera sequence, which consists of the aptamer sequence of S. aureus and the complementary sequence of MB, can form a hairpin structure due to the existence of intramolecular complementary regions. When S. aureus is present, it binds to the aptamer region of the chimera, opens the hairpin and unlocks the complementary sequence of MB. Subsequently, the MB is opened and intensive fluorescence signal is restored. To increase the sensitivity of the detection, signal amplification is achieved through strand displacement-based target recycling. With the catalysis of Nb. Bpu10I nicking endonuclease and Bsm DNA polymerase, the MB sequence can be cleaved and then elongated to form a complete duplex with the chimera, during which S. aureus is displaced from the chimera and proceeded to the next round of the reaction. This assay displays a linear correlation between the fluorescence intensity and the logarithm of the concentration of S. aureus within a broad concentration range from 80 CFU/mL to 8 × 10⁶ CFU/mL. The detection limit of 39 CFU/mL can be derived. The assay was applied to detect S. aureus in different water samples, and satisfactory recovery and repeatability were achieved. Hence the designed chimera sequence and established assay have potential application in environmental pollution monitoring.

Chronocoulometric aptamer based assay for staphylococcal enterotoxin B by target-triggered assembly of nanostructured dendritic nucleic acids on a gold electrode

A rapid and ultrasensitive method is described for the detection of staphylococcal enterotoxin B (SEB). It is based on the formation of a dendritic DNA superstructure by integrating (a) target-induced triggering of DNA release with (b) signal amplification by a hybridization chain reaction. Partially complementary pairing of aptamer and trigger DNA forms a duplex structure. The capture DNA is then placed on the surface of a gold electrode through gold-thiol chemistry. In the presence of SEB, the aptamer-target conjugate is compelled to form. This causes the release of trigger DNA owing to a strong competition with SEB. The trigger DNA is subsequently hybridized with the partial complementary sequences of the capture DNA to trigger HCR with three auxiliary DNA sequances (referred to as H1, H2, H3). Finally, the dendritic DNA superstructure is bound to hexaammineruthenium(III) cation by electrostatic adsorption and assembled onto the modified gold electrode. This produces an amplified electrochemical signal that is measured by chronocoulometry. Under optimal conditions, the charge difference increases linearly with the logarithm of the SEB concentrations in the range from 5 pg·mL^-1 to 100 ng·mL^-1 with a detection limit as low as 3 pg·mL^-1 (at S/N = 3). Graphical abstract An electrochemical switching strategy is presented for the sensitive detection of Staphylococcus enterotoxin B based on target-triggered assembly of dendritic nucleic acid nanostructures.

Emerging nano-biosensing with suspended MNP microbial extraction and EANP labeling

Emerging nano-biosensing with suspended MNP microbial extraction and EANP labeling may ensure a secure microbe-free food supply, as rapid response detection of microbial contamination is of utmost importance. Many biosensor designs have been proposed over the past two decades, covering a broad range of binding ligands, signal amplification, and detection mechanisms. These designs may consist of self-contained test strips developed from the base up with complicated nanoparticle chemistry and intricate ligand immobilization. Other methods use multiple step-wise additions, many based upon ELISA 96-well plate technology with fluorescent detection. In addition, many biosensors use expensive antibody receptors or DNA ligands. But many of these proposed designs are impracticable for most applications or users, since they don't FIRST address the broad goals of any biosensor: Field operability, Inexpensive, with Real-time detection that is both Sensitive and Specific to target, while being as Trouble-free as possible. Described in this review are applications that utilize versatile magnetic nanoparticles (MNP) extraction, electrically active nanoparticles (EANP) labeling, and carbohydrate-based ligand chemistry. MNP provide rapid pathogen extraction from liquid samples. EANP labeling improves signal amplification and expands signaling options to include optical and electrical detection. Carbohydrate ligands are inexpensive, robust structures that are increasingly synthesized for higher selectivity. Used in conjunction with optical or electrical detection of gold nanoparticles (AuNP), carbohydrate-functionalized MNP-cell-AuNP nano-biosensing advances the goal of being the FIRST biosensor of choice in detecting microbial pathogens throughout our food supply chain.