Impedimetric aptasensor for Staphylococcus aureus based on nanocomposite prepared from reduced graphene oxide and gold nanoparticles

Aptamer-enhanced ultrasensitive electrochemical detection of HER-2 in breast cancer diagnosis using ZnO tetrapod-K4PTC nanohybrids

Breast cancer continues to be a severe global health issue, emphasizing the critical need for accurate and timely detection and screening of large numbers of patients. This ailment places an enormous strain on healthcare resources and poses severe mortality risks for women globally if not addressed promptly. Conventional diagnostic techniques face obstacles such as expensive apparatus, intricate procedures, and long duration in stratification. Therefore, the development of point-of-care (PoC) devices that enable early detection of breast cancer is of utmost importance. This research article focuses on the development of an electrochemical based aptasensor for the detection of Human Epidermal Growth Factor Receptor 2 (HER-2) using the novel nanohybrid substrate material, which consists of a 3D Zinc Oxide Tetrapods (ZnOT) and Potassium Perylene Tetra Carboxylate (K4PTC). The analytical performance of the bio-nanoelectrode for detecting HER-2 was assessed using Square Wave Voltammetry (SWV) analysis. The developed nano-biosensor exhibited linear response in the range from 1 fg/mL - 10 µg/mL, and the overall limit of detection and sensitivity of the developed sensor is observed around 0.58 fg/mL and 2.08 µA/fg/mL/mm2, respectively. The shelf life of the sensor substrate is above one month in normal storage conditions. This study offers a base for the development of an efficient and sensitive breast cancer biomarker sensing platform, which has the potential to be implemented at a low cost for society and perform screening testing for breast cancer management in rural areas.

Ultrasensitive electroanalytical sensing platform using aptamer-conjugated V2CTx MXene for the detection of the HER-2 biomarker

Breast cancer is a leading cause of mortality among women globally, with the human epidermal growth factor receptor-2 (HER-2) serving as a vital biomarker for its diagnosis and management. In this study, an electrochemical aptasensor was developed using V2CTx MXene for the sensitive and selective quantification of HER-2. The sensor's electrochemical performance was evaluated through cyclic voltammetry (CV) and square wave voltammetry (SWV) that demonstrated a wide linear detection range of 1 ng mL-1 to 100 μg mL-1. The aptasensor achieved an exceptional detection limit of 0.36 ng mL-1 and a quantification limit of 1.96 ng mL-1 under optimized conditions. Furthermore, the sensor displayed excellent selectivity for HER-2 against other biomarkers and retained stability for 40 days, making it suitable for prolonged use. The high electrochemical response was attributed to the exceptional surface-to-volume ratio and conductivity of the V2CTx MXene, enabling efficient aptamer immobilization and signal enhancement. These findings highlight the potential of the developed aptasensor as a non-invasive, reliable, and cost-effective platform for early HER-2 detection, paving the way for improved breast cancer diagnosis and monitoring.

A novel ratiometric electrochemical aptasensor based on graphene quantum dots/Cu-MOF nanocomposite for the on-site determination of Staphylococcus aureus

The sensitive detection of Staphylococcus aureus (S. aureus) holds great practical importance for ensuring public health and food safety. In this study, a sensitivity and stability ratiometric electrochemical aptasensor using graphene quantum dots/[Cu2.5 (benzotriazole-5-COO)1.5 (benzotriazole-5-COOH)0.5 (μ-Cl)0.5 (μ3-OH)-(H2O)]·3 H2O nanocomposite (GQDs/Cu-MOF) was constructed for S. aureus detection. The GQDs enhanced the sensitivity of the electrochemical aptasensor due to their excellent conductivity and provided stability through their abundant carboxyl groups. The Cu-MOF, possessing electrical activity, not only enhanced the performance of the electrochemical aptasensor but also served as a signal label. The single-stranded DNA1 (S1) was immobilized on the surface of a GQDs/Cu-MOF/screen-printed carbon electrode (S1/GQDs/Cu-MOF/SPCE) as the sensing interface. Subsequently, the S1/GQDs/Cu-MOF/SPCE was hybridized with the probe DNA-ferrocene (S2-Fc), resulting in the generation of electrochemical signals from Cu-MOF (ICu-MOF) and S2-ferrocene (IS2-FC) within the system. However, the electron transfer performance of DNA at the sensing interface was compromised, leading to a reduction in the ICu-MOF. When S. aureus was present in the system, S2-Fc reacted with it and detached from the sensing surface, resulting in a gradual decrease in IS2-FC and an increase in ICu-MOF. Then a ratiometric electrochemical aptasensor was established for S. aureus detection with remarkable sensitivity (0.97 CFU·mL-1), excellent stability, and a broad linear range. Furthermore, the aptasensor was successfully applied to detect S. aureus in tap water, milk, Lonicera japonica, urine, and Zhangjiang River. Additionally, this aptasensor design can be adapted for the detection of other foodborne pathogens, which indicates that the design scheme of the aptasensor has good universality.

Parametric Cyclic Voltammetric Analysis of an Electrochemical Aptasensor for Staphylococcus aureus Iron-Regulated Surface Determinant Protein A Detection

Rapid and reliable detection of pathogens requires precise and optimized analytical techniques to address challenges in food safety and public health. This study focuses on the parametric characterization of an electrochemical aptasensor for Staphylococcus aureus (S. aureus) iron-regulated surface determinant protein A (IsdA) using cyclic voltammetry (CV) analysis, which offers a robust method for evaluating electrode modifications and electrochemical responses. Key parameters were optimized to ensure maximum sensitivity, including an aptamer concentration of 5 μM, an incubation time of 4 h, a potential range from -0.1 to 0.9 V, and a scan rate of 0.05 V/s. The aptasensor achieved stability and peak performance at pH 7.5 and 25 °C. These conditions were critical for detecting the IsdA protein as a biomarker of S. aureus. The aptasensor applicability was demonstrated by successfully detecting S. aureus in food samples such as milk and apple juice with high specificity and reliability. Zeta potential measurements confirmed the layer-by-layer charge dynamics of the AuNPs-aptamer-IsdA system. This work emphasizes the importance of CV in understanding the performance of the electrochemical sensor, and supports the aptasensor as a practical, sensitive, and portable tool for addressing critical gaps in foodborne pathogen detection.

Gold-Graphene Quantum Dot Hybrid Nanoparticle for Smart Diagnostics of Prostate Cancer

Prostate cancer is one of the most prevalent cancers afflicting men worldwide, often detected at advanced stages, leading to increased mortality rates. Addressing this challenge, we present an innovative approach employing electrochemical biosensing for early-stage prostate cancer detection. This study used Indium-Tin Oxide (ITO) as a substrate and a deposited gold-graphene quantum dot (Au-GQD) nanohybrid to establish electrochemical sensing platforms for DNA-hybridization assays. A capturing DNA probe, PCA3, was covalently immobilized on the surface of the Au-GQDs and deposited electrochemically onto the ITO electrode surface. The Au-GQDs enabled the capturing of the target PCA3 biomarker probe. The sensor achieved a limit of detection (LoD) of up to 211 fM and presented a linear detection range spanning 1 µM to 100 fM. A rapid 5-min response time was also achieved. The tested shelf life of the pre-immobilized sensor was approximately 19 ± 1 days, with pronounced selectivity for its intended target amidst various interferants. The sensing device has the potential to revolutionize prostate cancer management by facilitating early-stage detection and screening with enhanced treatment efficacy.

Bioreceptor modified electrochemical biosensors for the detection of life threating pathogenic bacteria: a review

The lack of reliable and efficient techniques for early monitoring to stop long-term effects on human health is an increasing problem as the pathogenesis effect of infectious bacteria is growing continuously. Therefore, developing an effective early detection technique coupled with efficient and continuous monitoring of pathogenic bacteria is increasingly becoming a global public health prime target. Electrochemical biosensors are among the strategies that can be utilized for accomplishing that goal with promising potential. In recent years, identifying target biological analytes by interacting with bioreceptors modified electrodes is among the most commonly used detection techniques in electrochemical biosensing strategies. The commonly employed bioreceptors are nucleic acid molecules (DNA or RNA), proteins, antibodies, enzymes, organisms, tissues, and biomimetic components such as molecularly imprinted polymers. Despite the advancement in electrochemical biosensing, developing a reliable and effective biosensor for detecting pathogenic bacteria is still in the infancy stage with so much room for growth. A major milestone in addressing some of the issues and improving the detection pathway is the investigation of specific bacterial detection techniques. The present study covers the fundamental concepts of electrochemical biosensors, human PB illnesses, and the latest electrochemical biosensors based on bioreceptor elements that are designed to detect specific pathogenic bacteria. This study aims to assist researchers with the most up-to-date research work in the field of bio-electrochemical pathogenic bacteria detection and monitoring.

Disposable electrochemical biosensors for the detection of bacteria in the light of antimicrobial resistance

Persistent and inappropriate use of antibiotics is causing rife antimicrobial resistance (AMR) worldwide. Common bacterial infections are thus becoming increasingly difficult to treat without the use of last resort antibiotics. This has necessitated a situation where it is imperative to confirm the infection to be bacterial, before treating it with antimicrobial speculatively. Conventional methods of bacteria detection are either culture based which take anywhere between 24 and 96 hor require sophisticated molecular analysis equipment with libraries and trained operators. These are difficult propositions for resource limited community healthcare setups of developing or less developed countries. Customized, inexpensive, point-of-care (PoC) biosensors are thus being researched and developed for rapid detection of bacterial pathogens. The development and optimization of disposable sensor substrates is the first and crucial step in development of such PoC systems. The substrates should facilitate easy charge transfer, a high surface to volume ratio, be tailorable by the various bio-conjugation chemistries, preserve the integrity of the biorecognition element, yet be inexpensive. Such sensor substrates thus need to be thoroughly investigated. Further, if such systems were made disposable, they would attain immunity to biofouling. This article discusses a few potential disposable electrochemical sensor substrates deployed for detection of bacteria for environmental and healthcare applications. The technologies have significant potential in helping reduce bacterial infections and checking AMR. This could help save lives of people succumbing to bacterial infections, as well as improve the overall quality of lives of people in low- and middle-income countries.

Review of Detection Limits for Various Techniques for Bacterial Detection in Food Samples

Foodborne illnesses can be infectious and dangerous, and most of them are caused by bacteria. Some common food-related bacteria species exist widely in nature and pose a serious threat to both humans and animals; they can cause poisoning, diseases, disabilities and even death. Rapid, reliable and cost-effective methods for bacterial detection are of paramount importance in food safety and environmental monitoring. Polymerase chain reaction (PCR), lateral flow immunochromatographic assay (LFIA) and electrochemical methods have been widely used in food safety and environmental monitoring. In this paper, the recent developments (2013-2023) covering PCR, LFIA and electrochemical methods for various bacterial species (Salmonella, Listeria, Campylobacter, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)), considering different food sample types, analytical performances and the reported limit of detection (LOD), are discussed. It was found that the bacteria species and food sample type contributed significantly to the analytical performance and LOD. Detection via LFIA has a higher average LOD (24 CFU/mL) than detection via electrochemical methods (12 CFU/mL) and PCR (6 CFU/mL). Salmonella and E. coli in the Pseudomonadota domain usually have low LODs. LODs are usually lower for detection in fish and eggs. Gold and iron nanoparticles were the most studied in the reported articles for LFIA, and average LODs were 26 CFU/mL and 12 CFU/mL, respectively. The electrochemical method revealed that the average LOD was highest for cyclic voltammetry (CV) at 18 CFU/mL, followed by electrochemical impedance spectroscopy (EIS) at 12 CFU/mL and differential pulse voltammetry (DPV) at 8 CFU/mL. LOD usually decreases when the sample number increases until it remains unchanged. Exponential relations (R2 > 0.95) between LODs of Listeria in milk via LFIA and via the electrochemical method with sample numbers have been obtained. Finally, the review discusses challenges and future perspectives (including the role of nanomaterials/advanced materials) to improve analytical performance for bacterial detection.

Research progress on the detection of foodborne pathogens based on aptamer recognition

Foodborne diseases caused by bacterial contamination are a serious threat to food safety and human health. The classical plate culture method has the problems of long detection cycle, low sensitivity and specificity, and complicated operation, which cannot meet the growing demand for rapid quantitative detection of pathogenic bacteria. The frequent outbreak of foodborne diseases has put forward higher requirements for rapid and simple detection technology of foodborne pathogens. Aptamer is a kind of oligonucleotide fragment that can recognize targets with the advantages of high affinity and good specificity. The target can be range from proteins, small molecules, cells bacteria, and even viruses. Herein, the latest advances in sensitive and rapid detection of foodborne pathogens based on aptamer recognition was reviewed. Special attention has been paid to the obtained sequences of aptamers to various foodborne pathogens, the optimization of sequences, and the mechanism of aptamer recognition. Then, the research progress of biosensors for the detection of pathogenic bacteria based on aptamer recognition were summarized. Some challenges and prospects for the detection of foodborne pathogens based on aptamer recognition were prospected. In summary, with the further deepening of aptamer research and improvement of detection technology, aptamer-based recognition can meet the needs of rapid, sensitive, and accurate detection in practical applications.

An electrochemical biosensor for Staphylococcus aureus detection based on a multilevel surface 3D micro/nanostructure

Detection of pathogens is one of the key concerns for hospitals, the food industry, water suppliers, or other environmental engineering practices because pathogens can cause a wide range of infectious risks. Staphylococcus aureus (S. aureus) is one of the most common pathogens that are hazardous to human health and its existence is an important index to the safety of food, environmental sanitation, or medical products. In this study, we prepared an electrode with designed surface multilevel 3D micro/nano protrusions for facile and efficient S. aureus detection. The existence of these multilevel protrusions enhanced the adsorption of S. aureus. Hence, the detection limit could be as low as 10 CFU mL-1. Furthermore, the electrode was also successfully used to detect S. aureus in actual samples, such as milk and artificial human tissue fluid. It was found that the recovery of the reported approach showed no significant difference from that of the traditional plate count method. However, compared with the plate count method, the detection process of our approach is much more time-saving and easy-operating. These advantages of the approach we report, such as high sensitivity, reliability, quickness, and user-friendliness, make it a potential platform for detecting S. aureus in relation to the food industry and clinical diagnosis.

Recent Advances in Electrochemical Biosensors for the Detection of Foodborne Pathogens: Current Perspective and Challenges

Foodborne pathogens cause many diseases and significantly impact human health and the economy. Foodborne pathogens mainly include Salmonella spp., Escherichia coli, Staphylococcus aureus, Shigella spp., Campylobacter spp. and Listeria monocytogenes, which are present in agricultural products, dairy products, animal-derived foods and the environment. Various pathogens in many different types of food and water can cause potentially life-threatening diseases and develop resistance to various types of antibiotics. The harm of foodborne pathogens is increasing, necessitating effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and culture plate, are time-consuming, labour-intensive and expensive and cannot satisfy the demands of rapid food testing. Therefore, new fast detection methods are urgently needed. Electrochemical biosensors provide consumer-friendly methods to quickly detect foodborne pathogens in food and the environment and achieve extensive accuracy and reproducible results. In this paper, by focusing on various mechanisms of electrochemical transducers, we present a comprehensive overview of electrochemical biosensors for the detection of foodborne pathogens. Furthermore, the review introduces the hazards of foodborne pathogens, risk analysis methods and measures of control. Finally, the review also emphasizes the recent research progress and solutions regarding the use of electrochemical biosensors to detect foodborne pathogens in food and the environment, evaluates limitations and challenges experienced during the development of biosensors to detect foodborne pathogens and discusses future possibilities.

Nanoarchitectonic E-Tongue of Electrospun Zein/Curcumin Carbon Dots for Detecting Staphylococcus aureusin Milk

We report a nanoarchitectonic electronic tongue made with flexible electrodes coated with curcumin carbon dots and zein electrospun nanofibers, which could detect Staphylococcus aureus(S. aureus) in milk using electrical impedance spectroscopy. Electronic tongues are based on the global selectivity concept in which the electrical responses of distinct sensing units are combined to provide a unique pattern, which in this case allowed the detection of S. aureus through non-specific interactions. The electronic tongue used here comprised 3 sensors with electrodes coated with zein nanofibers, carbon dots, and carbon dots with zein nanofibers. The capacitance data obtained with the three sensors were processed with a multidimensional projection technique referred to as interactive document mapping (IDMAP) and analyzed using the machine learning-based concept of multidimensional calibration space (MCS). The concentration of S. aureus could be determined with the sensing units, especially with the one containing zein as the limit of detection was 0.83 CFU/mL (CFU stands for colony-forming unit). This high sensitivity is attributed to molecular-level interactions between the protein zein and C-H groups in S. aureus according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Using machine learning and IDMAP, we demonstrated the selectivity of the electronic tongue in distinguishing milk samples from mastitis-infected cows from milk collected from healthy cows, and from milk spiked with possible interferents. Calibration of the electronic tongue can also be reached with the MCS concept employing decision tree algorithms, with an 80.1% accuracy in the diagnosis of mastitis. The low-cost electronic tongue presented here may be exploited in diagnosing mastitis at early stages, with tests performed in the farms without requiring specialized laboratories or personnel.

Conformational switching of aptamer biointerfacing graphene-gold nanohybrid for ultrasensitive label-free sensing of cardiac Troponin I

The development of hybrid biofunctionalized nanomaterials has emerged as an attractive substitute for development of advanced biosensing platforms with superior synergistic properties. Herein, we report a label-free ultrasensitive electrochemical aptasensor comprising nanohybrid of graphene oxide (GO) and aptamer conjugated gold nanoparticles (GNP-A) for detection of cardiac biomarker Troponin I (TnI). The GNP-A are homogenously arranged by self-assembly on GO sheet to construct nanohybrid (GO@GNP-A) onto which the biomarker protein is analysed. TnI interactions at the aptamer biointerfaced nanohybrid surface causes electrochemical signal enhancement probed by using a redox active molecule. The consecutive increase in current signal is strongly attributed to conformational switching of aptamer and charge neutralization at the interface induced by TnI binding. The sensitivity of the nanohybrid aptasensor platform was found to be 0.001 pg/mL. The study has been further substantiated in Acute Myocardial Infarction (AMI) clinical samples for usage towards early, sensitive and efficient point-of-care detection of TnI.

An Overview of the Public Health Challenges in Diagnosing and Controlling Human Foodborne Pathogens

Pathogens found in food are believed to be the leading cause of foodborne illnesses; and they are considered a serious problem with global ramifications. During the last few decades, a lot of attention has been paid to determining the microorganisms that cause foodborne illnesses and developing new methods to identify them. Foodborne pathogen identification technologies have evolved rapidly over the last few decades, with the newer technologies focusing on immunoassays, genome-wide approaches, biosensors, and mass spectrometry as the primary methods of identification. Bacteriophages (phages), probiotics and prebiotics were known to have the ability to combat bacterial diseases since the turn of the 20th century. A primary focus of phage use was the development of medical therapies; however, its use quickly expanded to other applications in biotechnology and industry. A similar argument can be made with regards to the food safety industry, as diseases directly endanger the health of customers. Recently, a lot of attention has been paid to bacteriophages, probiotics and prebiotics most likely due to the exhaustion of traditional antibiotics. Reviewing a variety of current quick identification techniques is the purpose of this study. Using these techniques, we are able to quickly identify foodborne pathogenic bacteria, which forms the basis for future research advances. A review of recent studies on the use of phages, probiotics and prebiotics as a means of combating significant foodborne diseases is also presented. Furthermore, we discussed the advantages of using phages as well as the challenges they face, especially given their prevalent application in food safety.

Applicability of a Green Nanocomposite Consisted of Spongin Decorated Cu2WO4(OH)2 and AgNPs as a High-Performance Aptasensing Platform in Staphylococcus aureus Detection

This study reports the synthesis of a nanocomposite consisting of spongin and its applicability in the development of an aptasensing platform with high performance. The spongin was carefully extracted from a marine sponge and decorated with copper tungsten oxide hydroxide. The resulting spongin-copper tungsten oxide hydroxide was functionalized by silver nanoparticles and utilized in electrochemical aptasensor fabrication. The nanocomposite covered on a glassy carbon electrode surface amplified the electron transfer and increased active electrochemical sites. The aptasensor was fabricated by loading of thiolated aptamer on the embedded surface via thiol-AgNPs linkage. The applicability of the aptasensor was tested in detecting the Staphylococcus aureus bacterium as one of the five most common causes of nosocomial infectious diseases. The aptasensor measured S. aureus under a linear concentration range of 10-10⁸ colony-forming units per milliliter and a limit of quantification and detection of 12 and 1 colony-forming unit per milliliter, respectively. The highly selective diagnosis of S. aureus in the presence of some common bacterial strains was satisfactorily evaluated. The acceptable results of the human serum analysis as the real sample may be promising in the bacteria tracking in clinical samples underlying the green chemistry principle.

An innovative dual recognition aptasensor for specific detection of Staphylococcus aureus based on Au/Fe3O4 binary hybrid

Pathogenic bacteria cause disease outbreaks and threaten human health, prompting the research on advanced detection assays. Herein, we developed a selective molecular imprinted aptasensor for sensitive and prompt quantitation of Staphylococcus aureus (S. aureus) bacteria. The aptasensor was constructed by immobilization of aptamer on gold nanoparticles modified magnetic nanoparticles (apt-AuNPs@ Fe₃O₄). A functional monomer (o-phenylenediamine, o-phen) was electro-polymerized on the surface of the as-synthesized nanocomposite in the presence of a template (S. aureus). After removing S. aureus, the formed imprinted sites were available to extract pathogenic bacteria from complicated matrices. The surface morphology of the as-fabricated nanocomposites was characterized using different spectroscopic and electrochemical methods. Moreover, we thoroughly evaluated factors affecting the synthesis and determination procedures. The molecular imprinted aptasensor exhibited a wide linear range of 10¹–10⁷ CFU mL⁻¹ with a Limit of Detection, LOD (signal to noise = 3) of 1 CFU mL⁻¹. The aptasensor detected S. aureus in milk, conduit water, and apple juice samples with good recoveries % and satisfactory relative standard deviations (RSDs %) values.

An Electroanalytical Flexible Biosensor Based on Reduced Graphene Oxide-DNA Hybrids for the Early Detection of Human Papillomavirus-16

Human Papilloma Virus 16 (HPV 16) is the well-known causative species responsible for triggering cervical cancer. When left undiagnosed and untreated, this disease leads to life-threatening events among the female populace, especially in developing nations where healthcare resources are already being stretched to their limits. Considering various drawbacks of conventional techniques for diagnosing this highly malignant cancer, it becomes imperative to develop miniaturized biosensing platforms which can aid in early detection of cervical cancer for enhanced patient outcomes. The current study reports on the development of an electrochemical biosensor based on reduced graphene oxide (rGO)/DNA hybrid modified flexible carbon screen-printed electrode (CSPE) for the detection of HPV 16. The carbon-coated SPEs were initially coated with rGO followed by probe DNA (PDNA) immobilization. The nanostructure characterization was performed using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and X-ray diffraction (XRD) techniques. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to study the electrochemical characterization of the nano-biohybrid sensor surface. The optimization studies and analytical performance were assessed using differential pulse voltammetry (DPV), eventually exhibiting a limit of detection (LoD) ~2 pM. The developed sensor was found to be selective solely to HPV 16 target DNA and exhibited a shelf life of 1 month. The performance of the developed flexible sensor further exhibited a promising response in spiked serum samples, which validates its application in future point-of-care scenarios.

An ultrasensitive sandwich-type electrochemical aptasensor using silver nanoparticle/titanium carbide nanocomposites for the determination of Staphylococcus aureus in milk

A novel sandwich-type electrochemical aptasensor for the detection of Staphylococcus aureus (S. aureus) was developed. S. aureus aptamers were self-assembled onto the surface of a glassy carbon electrode (GCE) modified with nanocomposites comprising titanium carbide embedded with silver nanoparticles (AgNPs@Ti₃C₂) through hydrogen bonds and the chelation interaction between phosphate groups and Ti ions. In addition, the self-assembled aptamers were immobilized on CuO/graphene (GR) nanocomposites via π-π stacking interactions to serve as a signal probe. In the presence of the target S. aureus, the sandwich-type recognition system reacted on the surface of GCE, and the CuO/GR nanocomposites catalyzed the hydrogen peroxide + hydroquinone reaction producing a strong current response. Under the optimal experimental conditions, the current response of the aptasensor was linearly correlated with the concentration of S. aureus (52-5.2 × 10⁷ CFU mL^-1) with a low detection limit of 1 CFU mL^-1. The aptasensor displayed good repeatability and excellent selectivity for S. aureus detection. Moreover, this aptasensor was applied to the detection of S. aureus in cow, sheep, and goat milk samples, affording recoveries ranging from 92.64 to 109.58%. This research provides a new platform for the detection of pathogenic bacteria and other toxic and harmful substances in food.

Recent Advances in Aptasensors For Rapid and Sensitive Detection of Staphylococcus Aureus

The infection of Staphylococcus aureus (S.aureus) and the spread of drug-resistant bacteria pose a serious threat to global public health. Therefore, timely, rapid and accurate detection of S. aureus is of great significance for food safety, environmental monitoring, clinical diagnosis and treatment, and prevention of drug-resistant bacteria dissemination. Traditional S. aureus detection methods such as culture identification, ELISA, PCR, MALDI-TOF-MS and sequencing, etc., have good sensitivity and specificity, but they are complex to operate, requiring professionals and expensive and complex machines. Therefore, it is still challenging to develop a fast, simple, low-cost, specific and sensitive S. aureus detection method. Recent studies have demonstrated that fast, specific, low-cost, low sample volume, automated, and portable aptasensors have been widely used for S. aureus detection and have been proposed as the most attractive alternatives to their traditional detection methods. In this review, recent advances of aptasensors based on different transducer (optical and electrochemical) for S. aureus detection have been discussed in details. Furthermore, the applications of aptasensors in point-of-care testing (POCT) have also been discussed. More and more aptasensors are combined with nanomaterials as efficient transducers and amplifiers, which appears to be the development trend in aptasensors. Finally, some significant challenges for the development and application of aptasensors are outlined.

Aptamer-Based Fluorescence Detection and Selective Disinfection of Salmonella Typhimurium by Using Hollow Carbon Nitride Nanosphere

Hollow carbon nitride nanosphere (HCNS) was synthesized via the hard template method to improve the fluorescence characteristics, drug delivery ability, and photocatalytic activity. Blue fluorescent HCNS was utilized as a quenching agent and an internal reference to combine with Cy5-labelled aptamer (Cy5-Apt), resulting in an off-on fluorescence aptasensing method for the detection of Salmonella typhimurium (S. typhimurium). Under optimum conditions, this fluorescence assay presented a linear range from 30 to 3 × 10⁴ CFU mL^-1 with a detection limit of 13 CFU mL^-1. In addition, HCNS was also used as a drug carrier to load chloramphenicol (Cap) molecules. The Cap-loading amount of HCNS could reach 550 μg mg^-1 within 24 h, whereas the corresponding Cap-release amount is 302.5 μg mg^-1 under acidic and irradiation conditions. The integration of photocatalyst with antibiotic could endow HCNS-Cap with better disinfection performance. The bactericidal efficiency of HCNS-Cap (95.0%) against S. typhimurium within 12 h was better than those of HCNS (85.1%) and Cap (72.9%). In addition, selective disinfection of S. typhimurium was further realized by decorating aptamer. Within 4 h, almost all S. Typhimurium were inactivated by HCNS-Cap-Apt, whereas only 13.3% and 48.2% of Staphylococcus aureus and Escherichia coli cells were killed, respectively. Therefore, HCNS is a promising bio-platform for aptamer-based fluorescence detection and selective disinfection of S. typhimurium.

Architecting of an aptasensor for the staphylococcus aureus analysis by modification of the screen-printed carbon electrode with aptamer/Ag-Cs-Gr QDs/NTiO2

Given the many issues bacterial infections cause to humans and the necessity for their detection, in this work we developed a robust aptasensor for prompt, ultrasensitive, and selective analysis of staphylococcus aureus bacterium (S. aureus). A nanocomposite of Ag nanoparticles, chitosan, graphene quantum dots, and nitrogen-doped TiO₂ nanoparticles (Ag-Cs-Gr QDs/NTiO₂) was synthesized, and thoroughly characterized by XRD, FT-IR, and FE-SEM spectroscopic methods. The surface of screen-printed carbon electrodes modified with Ag-Cs-Gr QDs/NTiO₂ nanocomposite was utilized as a compatible platform for aptamer attachment. The aptasensor accurately determined S. aureus in the dynamic range of 10-5 × 10⁸ CFU/mL with detection limit of 3.3 CFU/mL. The monitoring of the practical performance of aptasensor in human serum samples revealed its superiority over the conventional methods (relative recovery of 96.25-103.33%). The Ag-Cs-Gr QDs/NTiO₂-based aptasensor offers facile, biocompatibility, good repeatability, reproducibility (RSD = 3.66%), label free and stabile strategy for sensitive S. aureus analysis free from biomolecules interferences in actual specimens.

Electrochemical-based ''antibiotsensor'' for the whole-cell detection of the vancomycin-susceptible bacteria

In this study, we aim to develop an antibiotic-based biosensor platform 'Antibiotsensor' for the specific detection of gram-positive bacteria using vancomycin modified Screen Printed Gold Electrodes (SPGEs). Through this pathway, vancomycin molecules were first functionalized with thiol groups and characterized with quadrupole time of flight (q-TOF) mass spectroscopy analysis. Immobilization of thiolated vancomycin molecules (HS-Van) onto SPGEs was carried out based on self-assembled monolayer (SAM) phenomenon. Electrochemical impedance spectroscopy (EIS) was employed to test the detection and showed a considerable change in impedance value upon the binding of HS-Van molecules onto the electrode surface. Atomic Force Microscopy analysis indicated that SPGE was successfully modified upon the treatment with HS-Van molecules based on the shift in surface roughness from 173 ± 2 nm to 301 ± 3 nm. Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy proved the EIS and AFM results as well by showing characteristic peaks of immobilized HS-Van molecule. As a proof-of-concept, EIS-based susceptibility testing was performed using Escherichia coli, Staphylococcus aureus and Mycobacterium smegmatis bacteria to prove the specificity of obtained SPGE-Van. EIS data showed that the charge transfer resistance (R_ct) values changed from 1.08, 1.18 to 26.5, respectively, indicating that vancomycin susceptible S. aureus was successfully attached onto SPGE-Van surface strongly, while vancomycin resistance E. coli and M. smegmatis did not show any significant attachment properties. In addition, different concentration (10⁸-10 CFU/mL) of S. aureus was performed to investigate sensitivity of proposed sensor platform. Limit of detection and limit of quantitation was calculated as 10^1.58 and 10^4.81 CFU/mL, respectively. Scanning electron microscopy (SEM) analysis also confirmed that only S. aureus bacteria was attached to the surface in a dense monolayer distribution. We believe that the proposed approach is selective and sensitive towards the whole-cell detection of vancomycin-susceptible bacteria and can be modified for different purposes in the future.

Fabrication of an ultrasensitive aptasensor for precise electrochemical detection of the trace amounts of streptomycin in milk

Designing a sensitive method for the detection of streptomycin residues in animal products is essential for controlling consumer health risk. In this study, a high-purity pencil lead graphite electrode coated with inner graphene layers and outer surface-adsorbed gold nanoparticles attached to streptomycin-specific thiolated aptamer was used as an electrochemical aptasensor. The aptasensor electrode fabrication steps were investigated by scanning electron microscope (SEM) and Fourier-transform infrared spectrophotometer (FTIR). Moreover, aptasensor performance during fabrication and binding of aptamer to streptomycin were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. After the binding of sreptomycin to it's specific aptamer as a component of the aptasensor a decrease in the current and an increase in the charge transfer resistance (R_ct) were recorded using the above-mentioned techniques. Under optimal conditions, the novel ultra-sensetive designed aptansensor detects streptomycin in the range of  10^-8 to  10^-16 M with a LOD of 0.8×10^-18 M. The aptansensor demonstrates a high selectivity, good reproducibility and acceptable stability for the specific detection of streptomycin. According to the results, the manufactured aptansensor is a fast, low-cost, highly sensitive and selective device and thus the aptasensor can detect the trace amounts of streptomycin in milk in dairy industries.

A Low-Field Magnetic Resonance Imaging Aptasensor for the Rapid and Visual Sensing of Pseudomonas aeruginosa in Food, Juice, and Water

In this work, we present a low-field magnetic resonance imaging (LF-MRI) aptasensor based on the difference in magnetic behavior of two magnetic nanoparticles with diameters of 10 (MN₁₀) and 400 nm (MN₄₀₀) for the rapid detection of Pseudomonas aeruginosa (P. aeruginosa). First, specific anti-P. aeruginosa aptamers were covalently immobilized onto magnetic nanoparticles via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide chemistry for the capture of the target bacteria. In the presence of P. aeruginosa, an MN₁₀-bacteria-MN₄₀₀ (MBM) complex was formed after binding between the aptamers on magnetic nanoparticles and P. aeruginosa cells. When a magnetic field was applied, the MBM complex and free MN₄₀₀ were rapidly magnetically separated, and free MN₁₀ left in the solution worked as a T₂ (transverse relaxation time) single readout in MRI measurement. Under optimum conditions, the LF-MRI platform provides both image analysis and quantitative detection of P. aeruginosa, with a detection limit of 100 cfu/mL. The feasibility and specificity of the aptasensor were demonstrated in detecting real food, orange juice, and drinking water samples and validated using plate counting methods.

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing.

Self-Assembled DNA Nanoflowers Triggered by a DNA Walker for Highly Sensitive Electrochemical Detection of Staphylococcus aureus

With the development of DNA nanotechnology, DNA has been widely used to construct a variety of nanomachines. Among them, a DNA walker is a unique nanomachine that can move continuously along a specific orbit to fulfill diverse functions. In this paper, a dual signal amplification electrochemical biosensor based on a DNA walker and DNA nanoflowers is constructed for high sensitivity detection of Staphylococcus aureus (S. aureus). Two groups of double-stranded DNA are modified on the surface of a gold electrode. The binding of S. aureus with its aptamer induces the disintegration of the long double strands and releases the DNA walker. With the help of exonuclease III (Exo III), the DNA walker moves along the electrode surface and continuously hydrolyzes the anchored short double strands. The introduction of a specially customized circular DNA and phi29 DNA polymerase initiates the rolling circle amplification (RCA) reaction. DNA nanoflowers are formed at high local concentration of DNA in the solution, which provide binding sites for electroactive methylene blue (MB) and thus produce intense signal. Under the best conditions, the current response is linearly related to the logarithm of the concentration of S. aureus ranging from 60 to 6 × 10⁷ CFU/mL, and the detection limit is 9 CFU/mL. In addition, the proposed biosensor has achieved satisfactory results in the detection of actual water samples and diluted honey samples, which confirm the practicability of the biosensor and its application potential in environmental monitoring and food safety.

Advances in nanomaterial-based electrochemical biosensors for the detection of microbial toxins, pathogenic bacteria in food matrices

There is a growing demand to protect food products against the hazard of microbes and their toxins. To satisfy such goals, it is important to develop highly sensitive, reliable, sophisticated, rapid, and cost-effective sensing techniques such as electrochemical sensors/biosensors. Although diverse forms of nanomaterials (NMs)-based electrochemical sensing methods have been introduced in markets, the reliability of commercial products is yet insufficient to meet the practical goal. In this review, we focused on: 1) sources of pathogenic microbes and their toxins; 2) possible routes of their entrainment in food, and 3) current development of NM-based biosensors to realize real-time detection of the target analytes. At last, future prospects and challenges in this research field are discussed.

Electrochemical immunosensor for determination of Staphylococcus aureus bacteria by IgY immobilized on glassy carbon electrode with electrodeposited gold nanoparticles

A new ultrasensitive immunosensor is proposed based on the covalently attached anti-protein A antibody (IgY) on deposited gold nanoparticle (AuNP)-modified glassy carbon electrode (GCE) for the electrochemical measurement of Staphylococcus aureus (S. aureus). Chicken IgY as a capture antibody provides highly selective and specific binding to the target bacteria and selectively captures the S. aureus in its three-dimensional space. Due to that it can eliminate the interference from protein G-producing Streptococcus. In addition, the electron-transfer characteristic of [Fe(CN)₆]^4-/3- is hindered by this combination; as it is reflected on the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) curves. The proposed immunosensor displays a wide linear dynamic range from 10 to 10⁷ CFU mL^-1 with a detection limit of 3.3 CFU mL^-1 with RSD 3.0%. It is capable to accurately determine S. aureus in milk and human blood serum as a complex matrix sample with satisfactory recovery of ∼ 97-103%. The immunosensor also displays high selectivity over other bacteria and acceptable stability. Presumably, our study can be regarded as the first one to report chicken IgY in order to detect S. aureus based on an electrochemical method.Graphical abstract.

Controlled molecular architectures in microfluidic immunosensors for detecting Staphylococcus aureus

Detection of pathogenic microorganisms is essential for food quality control and diagnosis of various diseases, which is currently performed with high-cost, sophisticated methods. In this paper, we report on a low-cost detection method based on impedance spectroscopy to detect Staphylococcus aureus (S. aureus). The immunosensors were made with microfluidic devices made of interdigitated electrodes coated with layer-by-layer (LbL) films of chitosan and chondroitin sulfate, on which a layer of anti-S. aureus antibodies was adsorbed. The limit of detection was 2.83 CFU mL-1 with a limit of quantification of 9.42 CFU mL-1 for immunosensors with 10-bilayer LbL films. This level of sensitivity is sufficient to detect traces of bacteria that cause mastitis in milk, which we have confirmed by distinguishing milk samples containing various concentrations of S. aureus from pure milk and milk contaminated with Escherichia coli (E. coli) and Salmonella. Distinction of these samples was made possible by projecting the electrical impedance data with the interactive document mapping (IDMAP) technique. The high sensitivity and selectivity are attributed to the highly specific interaction with anti-S. aureus antibodies captured with polarization-modulated reflection absorption spectroscopy (PM-IRRAS), with adsorption on the antibodies explained with the Langmuir-Freundlich model. Since these immunosensors are stable for up to 25 days and detection measurements can be made within minutes, the methodology proposed is promising for monitoring S. aureus contamination in the food industry and hospitals, and in detecting bovine mastitis.

Impedimetric Aptamer-Based Biosensors: Applications

Impedimetric aptamer-based biosensors show high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors for applications in biotechnology. We detail on analytes relevant in medical and environmental biotechnology as well as food control, for which aptamer-based impedimetric biosensors were developed. The reviewed biosensors are examined for their performance, including sensitivity, selectivity, response time, and real sample validation. Additionally, the benefits and challenges of impedimetric aptasensors are summarized.

3D-Printed Flow Cells for Aptamer-Based Impedimetric Detection of E. coli Crooks Strain

Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of Escherichia coli (E. coli) Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications.

Ultrasensitive peptide-based multiplexed electrochemical biosensor for the simultaneous detection of Listeria monocytogenes and Staphylococcus aureus

A novel electrochemical biosensor is reported for simultaneous detection of two of the most common food-borne pathogens: Listeria monocytogenes and Staphylococcus aureus. The biosensor is composed of an array of gold nanoparticles-modified screen-printed carbon electrodes on which magnetic nanoparticles coupled to specific peptides were immobilized via streptavidin-biotin interaction. Taking advantage of the proteolytic activities of the protease enzymes produced from the two bacteria on the specific peptides, the detection was achieved in 1 min. The detection was realized by measuring the percentage increase of the square wave voltammetric peak current at 0.1 V versus a Ag/AgCl reference electrode in ferro/ferricyanide redox couple after incubation with the bacteria protease. The integration of the specificity of the bacterial enzymes towards their peptide substrates with the sensitivity of the electrochemical detection on the sensor array allows the rapid, sensitive and selective quantification of the two bacteria. Outstanding sensitivities were achieved using this biosensor array platform with limit of detection of 9 CFU mL^-1 for Listeria monocytogenes and 3 CFU mL^-1 for Staphylococcus aureus. The multiplexing capability and selectivity of the array voltammetric biosensor were demonstrated by analysing samples of Staphylococcus aureus, Listeria monocytogenes or E. coli and also containing a mixture of two or three bacteria. Using this biosensor, the two bacteria were successfully quantified simultaneously in one step without the need for DNA extraction or amplification techniques. This platform offers promise for rapid, simple and cost-effective simultaneous detection of various bacteria. Graphical abstract.

Size-Dependent Modulation of Polydopamine Nanospheres on Smart Nanoprobes for Detection of Pathogenic Bacteria at Single-Cell Level and Imaging-Guided Photothermal Bactericidal Activity

Pathogenic bacterial fouling in agriculture and food-associated products poses mounting food safety concerns today. Efficient integration of precise tracking and on-demand bacterial killing to achieve the source control of pathogenic bacteria at the single-cell level is one of the most valuable antifouling methods for safeguarding food safety but remains unexplored. Here, we report an all-in-one design strategy as a proof of concept to establish a stimuli-responsive nanoprobe PDANSs-FAM-Apt for the detection of Staphylococcus aureus (S. aureus) at the single-cell level, which could be capable of guiding the on-demand photothermal killing of bacteria upon near-infrared (NIR) light irradiation. By examining the size-dependent modulation of the fluorescence resonance energy transfer efficiency to polydopamine nanospheres (PDANSs), PDANSs-FAM-Apt was finally assembled by 6-carboxyfluorescein-terminated S. aureus, binding the aptamer (FAM-Apt) and PDANSs at ∼258 nm through π-π stacking interactions. As a result, PDANSs-FAM-Apt exhibits a remarkable fluorescence enhancement (∼261-fold) to S. aureus with a satisfactory detection limit of 1.0 cfu/mL, allowing for assay at the single-cell level and thus ultralow background fluorescence imaging of S. aureus as well as its biofilms. Moreover, PDANSs-FAM-Apt shows a high photothermal bactericidal property upon NIR light irradiation, endowing it with the strong capacity to efficiently produce heat for destroying S. aureus and its biofilms with the guidance of imaging results. This work emphasizes the versatility of using the combination of stimuli-responsive fluorescence imaging dependent on the PDANS size modulation and NIR light-activated photothermal antibacterial activity to design stimuli-responsive nanoprobes with an improved precision for pathogenic bacteria monitoring and source controlling, which opens a promising antifouling avenue to eliminate bacteria and disrupt bacterial biofilms in agriculture and food-related industries.

Electrochemical biosensors for pathogen detection

Recent advances in electrochemical biosensors for pathogen detection are reviewed. Electrochemical biosensors for pathogen detection are broadly reviewed in terms of transduction elements, biorecognition elements, electrochemical techniques, and biosensor performance. Transduction elements are discussed in terms of electrode material and form factor. Biorecognition elements for pathogen detection, including antibodies, aptamers, and imprinted polymers, are discussed in terms of availability, production, and immobilization approach. Emerging areas of electrochemical biosensor design are reviewed, including electrode modification and transducer integration. Measurement formats for pathogen detection are classified in terms of sample preparation and secondary binding steps. Applications of electrochemical biosensors for the detection of pathogens in food and water safety, medical diagnostics, environmental monitoring, and bio-threat applications are highlighted. Future directions and challenges of electrochemical biosensors for pathogen detection are discussed, including wearable and conformal biosensors, detection of plant pathogens, multiplexed detection, reusable biosensors for process monitoring applications, and low-cost, disposable biosensors.

An overview and future prospects on aptamers for food safety

Introduction

Many bacteria are responsible for infections in humans and plants, being found in vegetables, water, and medical devices. Most bacterial detection methods are time-consuming and take days to give the result. Aptamers are a promising alternative for a quick and reliable measurement technique to detect bacteria present in food products. Selected aptamers are DNA or RNA oligonucleotides that can bind with bacteria or other molecules with affinity and specificity for the target cells by the SELEX or cell-SELEX technique. This method is based on some rounds to remove the non-ligand oligonucleotides, leaving the aptamers specific to bind to the selected bacteria. Compared with conventional methodologies, the detection approach using aptamers is a rapid, low-cost form of analysis.

Objective

This review summarizes obtention methods and applications of aptamers in the food industry and biotechnology. Besides, different techniques with aptamers are presented, which enable more effective target detection.

Conclusion

Applications of aptamers as biosensors, or the association of aptamers with nanomaterials, may be employed in analyses by colorimetric, fluorescence, or electrical devices. Additionally, more efficient ways of sample preparation are presented, which can support food safety to provide human health, with a low-cost method for contaminant detection.

Key points • Aptamers are promising for detecting contaminants outbreaks. • Studies are needed to identify aptamers for different targets.

Inhibitory effects of aptamer targeted teicoplanin encapsulated PLGA nanoparticles for Staphylococcus aureus strains

Emergence of resistance to traditional antibiotic treatments necessitates alternative delivery systems. Teicoplanin is a glycopeptide antibiotic used in the treatments of serious infections caused by Gram-positive bacteria, including Methicillin Resistant Staphylococcus aureus (MRSA). One strategy to keep up with antibiotic resistance development is to limit dose and amount during treatments. Targeted delivery systems of antibiotics have been suggested as a mechanism to slow-down the evolution of resistance and to increase efficiency of the antimicrobials on already resistant pathogens. In this study, we report teicoplanin delivery nanoparticles of Poly Lactic-co-Glycolic Acid (PLGA), which are functionalized with S. aureus specific aptamers. A 32-fold decrease in minimum inhibitory concentration (MIC) values of teicoplanin for S. aureus was demonstrated for susceptible strains and about 64-fold decline in MIC value was achieved for moderately resistant clinical isolates of MRSA upon teicoplanin treatment with aptamer-PLGA nanoparticles. Although teicoplanin delivery in PLGA nanoparticles without targeting demonstrated eightfold decrease in MIC of susceptible strains of S. aureus and S. epidermidis and twofold in MIC of resistant strains, the aptamer targeting specifically decreased MIC for S. aureus, but not for S. epidermidis. Therefore, aptamer-targeted PLGA delivery of antibiotic can be an attractive alternative to combat with some of the multi-drug resistant bacterial pathogens.

Recent advances in two-dimensional-material-based sensing technology toward health and environmental monitoring applications

Monitoring harmful and toxic chemicals, gases, microorganisms, and radiation has been a challenge to the scientific community for the betterment of human health and environment. Two-dimensional (2D)-material-based sensors are highly efficient and compatible with modern fabrication technology, which yield data that can be proficiently used for health and environmental monitoring. Graphene and its oxides, black phosphorus (BP), transition metal dichalcogenides (TMDCs), metal oxides, and other 2D nanomaterials have demonstrated properties that have been alluring for the manufacture of highly sensitive sensors due to their unique material properties arising from their inherent structures. This review summarizes the properties of 2D nanomaterials that can provide a platform to develop high-performance sensors. In this review, we have also discussed the advances made in the field of infrared photodetectors and electrochemical sensors and how the structural properties of 2D nanomaterials affect sensitivity and performance. Further, this review highlights 2D-nanomaterial-based electrochemical sensors that can be used to check for contaminations from heavy metals, organic/inorganic compounds, poisonous gases, pesticides, bacteria, antibiotics, etc., in water or air, which are severe risks to human wellbeing as well as the environment. Moreover, the limitations, future prospects, and challenges for the development of sensors based on 2D materials are also discussed for future advancements.

A dual electrochemical/colorimetric magnetic nanoparticle/peptide-based platform for the detection of Staphylococcus aureus

Rapid and economical biosensor for Staphylococcus aureus, one of the main causes of food-borne illness, was developed based on dual colorimetric and electrochemical detection.

Review of Electrochemical DNA Biosensors for Detecting Food Borne Pathogens

The vital importance of rapid and accurate detection of food borne pathogens has driven the development of biosensor to prevent food borne illness outbreaks. Electrochemical DNA biosensors offer such merits as rapid response, high sensitivity, low cost, and ease of use. This review covers the following three aspects: food borne pathogens and conventional detection methods, the design and fabrication of electrochemical DNA biosensors and several techniques for improving sensitivity of biosensors. We highlight the main bioreceptors and immobilizing methods on sensing interface, electrochemical techniques, electrochemical indicators, nanotechnology, and nucleic acid-based amplification. Finally, in view of the existing shortcomings of electrochemical DNA biosensors in the field of food borne pathogen detection, we also predict and prospect future research focuses from the following five aspects: specific bioreceptors (improving specificity), nanomaterials (enhancing sensitivity), microfluidic chip technology (realizing automate operation), paper-based biosensors (reducing detection cost), and smartphones or other mobile devices (simplifying signal reading devices).

Rapid and sensitive detection of Salmonella with reduced graphene oxide-carbon nanotube based electrochemical aptasensor

Rapid detection of foodborne pathogens is crucial as ingestion of contaminated food products may endanger human health. Thus, the objective of this study was to develop a biosensor using reduced graphene oxide-carbon nanotubes (rGO-CNT) nanocomposite via the hydrothermal method for accurate and rapid label-free electrochemical detection of pathogenic bacteria such as Salmonella enterica. The rGO-CNT nanocomposite was characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction and transmission electron microscopy. The nanocomposite was dropped cast on the glassy carbon electrode and further modified with amino-modified DNA aptamer. The resultant ssDNA/rGO-CNT/GCE aptasensor was then used to detect bacteria by using differential pulse voltammetry (DPV) technique. Synergistic effects of aptasensor was evident through the combination of enhanced electrical properties and facile chemical functionality of both rGO and CNT for the stable interface. Under optimal experimental conditions, the aptasensor could detect S. Typhimurium in a wide linear dynamic range from 10¹ until 10⁸ cfu mL^-1 with a 10¹ cfu mL^-1 of the limit of detection. This aptasensor also showed good sensitivity, selectivity and specificity for the detection of microorganisms. Furthermore, we have successfully applied the aptasensor for S. Typhimurium detection in real food samples.

Enzyme-free hybridization chain reaction-based signal amplification strategy for the sensitive detection of Staphylococcus aureus

In this study, based on hybridization chain reaction (HCR) amplification and graphene oxide (GO), we developed a facile enzyme-free signal amplification strategy for sensitive detection of Staphylococcus aureus (S. aureus). Two hairpin probes (HP₁ and HP₂) labeled by fluorophore 6-carboxyfluorescein (FAM) are designed. The HP₁ and HP₂ can not only trigger to the HCR but also form a long nicked double strand DNA (dsDNA) with the target (16S rRNA). In the absence of target (16 s RNA), the free FAM-labeled HP1 and HP2 are adsorbed by the GO via π-π stacking, the fluorescence signal is quenched. In the presence of target (16 s RNA), the HCR is triggered and dsDNA complexes are generated. As a result, the fluorescence signal can be strongly amplified by the synergistic effect of FAM and the dsDNA dye SYBR Green I. Based on this mechanism, a fluorescence method is designed for the detection of 16S rRNA of S. aureus. Under the optimal conditions, it has low detection limit (50 pM) and a linear response in a concentration range of 50 pM to 100 nM for 16S rRNA. Furthermore, this method has also been successfully applied to the detection of S. aureus in milk sample with the detection limit of 4 × 10² CFU·mL^-1.