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

Graphene oxide/Cu-MOF-based electrochemical immunosensor for the simultaneous detection of Mycoplasma pneumoniae and Legionella pneumophila antigens in water

The combination of copper-metal organic framework (Cu-MOF) with graphene oxide (GO) has received growing interest in electrocatalysis, energy storage and sensing applications. However, its potential as an electrochemical biosensing platform remains largely unexplored. In this study, we introduce the synthesis of GO/Cu-MOF nanocomposite and its application in the simultaneous detection of two biomarkers associated with lower respiratory infections, marking the first instance of its use in this capacity. The physicochemical properties and structural elucidation of this composite were studied with the support of XRD, FTIR, SEM and electrochemical techniques. The immunosensor was fabricated by drop casting the nanocomposite on dual screen-printed electrodes followed by functionalization with pyrene linker. The covalent immobilization of the monoclonal antibodies of the bacterial antigens of Mycoplasma pneumoniae (M. pneumoniae; M. p.) and Legionella pneumophila (L. pneumophila; L. p.) was achieved using EDC-NHS chemistry. The differential pulse voltammetry (DPV) signals of the developed immunosensor platform demonstrated a robust correlation across a broad concentration range from 1 pg/mL to 100 ng/mL. The immunosensor platform has shown high degree of selectivity against antigens for various respiratory pathogens. Moreover, the dual immunosensor was successfully applied for the detection of M. pneumoniae and L. pneumophila antigens in spiked water samples showing excellent recovery percentages. We attribute the high sensitivity of the immunosensor to the enhanced electrocatalytic characteristics, stability and conductivity of the GO-MOF composite as well as the synergistic interactions between the GO and MOF. This immunosensor offers a swift analytical response, simplicity in fabrication and instrumentation, rendering it an appealing platform for the on-field monitoring of pathogens in environmental samples.

Gold nanoparticles-based biosensors: pioneering solutions for bacterial and viral pathogen detection-a comprehensive review

Gold Nanoparticles (AuNPs) have gained significant attention in biosensor development due to their unique physical, chemical, and optical properties. When incorporated into biosensors, AuNPs offer several advantages, including a high surface area-to-volume ratio, excellent biocompatibility, ease of functionalization, and tunable optical properties. These properties make them ideal for the detection of various biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Traditional methods for detecting bacteria and viruses, such as RT-PCR and ELISA, often suffer from complexities, time consumption, and labor intensiveness. Consequently, researchers are continuously exploring novel devices to address these limitations and effectively detect a diverse array of infectious pathogenic microorganisms. In light of these challenges, nanotechnology has been instrumental in refining the architecture and performance of biosensors. By leveraging advancements in nanomaterials and strategies of biosensor fabrication the sensitivity and specificity of biosensors can be enhanced, enabling more precise detection of pathogenic bacteria and viruses. This review explores the versatility of AuNPs in detecting a variety of biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Furthermore, it evaluates recent advancements in AuNPs-based biosensors for the detection of pathogens, utilizing techniques such as optical biosensors, lateral flow immunoassays, colorimetric immunosensors, electrochemical biosensors, and fluorescence nanobiosensors. Additionally, the study discusses the existing challenges in the field and proposes future directions to improve AuNPs-based biosensors, with a focus on enhancing sensitivity, selectivity, and their utility in clinical and diagnostic applications.

Controllable self-cleaning FET self-assembled RNA-cleaving DNAzyme based DNA nanotree for culture-free Staphylococcus aureus detection

Staphylococcus aureus (SA) poses a serious risk to human and animal health, necessitating a low-cost and high-performance analytical platform for point-of-care diagnostics. Cellulose paper-based field-effect transistors (FETs) with RNA-cleaving DNAzymes (RCDs) can fulfill the low-cost requirements, however, its high hydrophilicity and lipophilicity hinder biochemical modification and result in low sensitivity, poor mechanical stability and poor fouling performance. Herein, we proposed a controllable self-cleaning FET to simplify biochemical modification and improve mechanical stability and antifouling performance. Then, we constructed an RCD-based DNA nanotree to significantly enhance the sensitivity for SA detection. For controllable self-cleaning FET, 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane based-polymeric nanoparticles were synthesized to decorate cellulose paper and whole carbon nanofilm wires. O2 plasma was applied to regulate to reduce fluorocarbon chain density, and then control the hydrophobic-oleophobic property in sensitive areas. Because negatively charged DNA affected the sensitivity of semiconducting FETs, three Y-shaped branches with low-cost were designed and applied to synthesize an RCD-based DNA-Nanotree based on similar DNA-origami technology, which further improved the sensitivity. The trunk of DNA-Nanotree was composed of RCD, and the canopy was self-assembled using multiple Y-shaped branches. The controllable self-cleaning FET biosensor was applied for SA detection without cultivation, which had a wide linear range from 1 to 105 CFU/mL and could detect a low value of 1 CFU/mL.

Point-of-Care Electrochemical Immunosensor Applied against Nosocomial Infection: Staphylococcus aureus Detection in Human Hand Skin

Staphylococcus aureus is an important pathogen that causes nosocomial infections, resulting in unacceptable morbidity and mortality rates. In this work, we proposed the construction of a nanostructured ZnO-based electrochemical immunosensor for qualitative and semiquantitative detection of S. aureus using simple methods for growing zinc oxide nanorods (ZnO NRs) on a sensor board and immobilizing the anti-S. aureus antibody on ZnO NRs through cystamine and glutaraldehyde. The immunosensor detected S. aureus in the 103-107 colony-forming unit (CFU) mL-1 range and showed a limit of detection (LoD) around 0.792 × 103 CFU mL-1. Beyond a satisfactory LoD, the developed immunosensor presented other advantages, such as high versatility for point-of-care assays and a suitable selective factor that admits the detection of the S. aureus concentration range in human hand skin after washing. Moreover, the immunosensor showed the potential to be an excellent device to control nosocomial infection by detecting the presence of S. aureus in human hand skin.

Selection of ssDNA aptamers and construction of aptameric electrochemical biosensor for the detection of Giardia intestinalis trophozoite protein

Giardia intestinalis is one of the most widespread intestinal parasites and is considered a major cause of epidemic or sporadic diarrhea worldwide. In this study, we aimed to develop a rapid aptameric diagnostic technique for G. intestinalis infection. First, the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) process generated DNA aptamers specific to a recombinant protein of the parasite's trophozoite. Ten selection rounds were performed; each round, the DNA library was incubated with the target protein conjugated to Sepharose beads. Then, the unbound sequences were removed by washing and the specific sequences were eluted and amplified by Polymerase Chain Reaction (PCR). Two aptamers were selected, and the dissociation constants (Kd), were determined as 2.45 and 16.95 nM, showed their high affinity for the G. intestinalis trophozoite protein. Subsequently, the aptamer sequence T1, which exhibited better affinity, was employed to develop a label-free electrochemical biosensor. A thiolated aptamer was covalently immobilized onto a gold screen-printed electrode (SPGE), and the binding of the targeted protein was monitored using square wave voltammetry (SWV). The developed aptasensor enabled accurate detection of the G. intestinalis recombinant protein within the range of 0.1 pg/mL to 100 ng/mL, with an excellent sensitivity (LOD of 0.35 pg/mL). Moreover, selectivity studies showed a negligible cross-reactivity toward other proteins such as bovine serum albumin, globulin, and G. intestinalis cyst protein.

1D ZnO-Au nanocomposites as label-free photoluminescence immunosensors for rapid detection of Listeria monocytogenes

In this study, we explore the potential of 1D ZnO-Au nanocomposites as innovative label-free photoluminescence (PL) immunosensors for rapidly detecting Listeria monocytogenes, a significant concern in food safety. We synthesized ZnO nanorods (ZnO_NR) and nanowires (ZnO_NW), followed by Au deposition to create ZnO_NR/Au and ZnO_NW/Au nanocomposites. Our analyses, including SEM, TEM, Raman spectroscopy, and photoluminescence (PL), revealed distinct structural and optical properties of these nanocomposites, especially noting the superior crystallinity and stability of ZnO_NR/Au. The biosensor performance was evaluated through PL sensitivity to Anti-Listeria antibodies, demonstrating that ZnO_NR with higher concentration of Au nanoparticles exhibited higher sensitivity and a lower limit of detection (LOD), attributed to a greater density of Listeria binding sites. The developed biosensor demonstrated a remarkable limit of detection (LOD) of 8.3 × 102 CFU/mL, rivaling or surpassing conventional culture-based methods and some molecular techniques. This research underscores the critical role of Au deposition duration in optimizing biosensor performance and presents a promising advancement in rapid and sensitive Listeria detection, with significant implications for enhancing food safety protocols.

Nanomaterial-based methods for sepsis management

Sepsis is a serious disease caused by an impaired host immune response to infection, resulting in organ dysfunction, tissue damage and is responsible for high in-hospital mortality (approximately 20%). Recently, WHO documented sepsis as a global health priority. Nevertheless, there is still no effective and specific therapy for clinically detecting sepsis. Nanomaterial-based approaches have appeared as promising tools for identifying bacterial infections. In this review, recent biosensors are introduced and summarized as nanomaterial-based platforms for sepsis management and severe complications. Biosensors can be used as tools for the diagnosis and treatment of sepsis and as nanocarriers for drug delivery. In general, diagnostic methods for sepsis-associated bacteria, biosensors developed for this purpose are presented in detail, and their strengths and weaknesses are discussed. In other words, readers of this article will gain a comprehensive understanding of biosensors and their applications in sepsis management.

Progress and Challenge of Sensors for Dairy Food Safety Monitoring

One of the most consumed foods is milk and milk products, and guaranteeing the suitability of these products is one of the major concerns in our society. This has led to the development of numerous sensors to enhance quality controls in the food chain. However, this is not a simple task, because it is necessary to establish the parameters to be analyzed and often, not only one compound is responsible for food contamination or degradation. To attempt to address this problem, a multiplex analysis together with a non-directed (e.g., general parameters such as pH) analysis are the most relevant alternatives to identifying the safety of dairy food. In recent years, the use of new technologies in the development of devices/platforms with optical or electrochemical signals has accelerated and intensified the pursuit of systems that provide a simple, rapid, cost-effective, and/or multiparametric response to the presence of contaminants, markers of various diseases, and/or indicators of safety levels. However, achieving the simultaneous determination of two or more analytes in situ, in a single measurement, and in real time, using only one working 'real sensor', remains one of the most daunting challenges, primarily due to the complexity of the sample matrix. To address these requirements, different approaches have been explored. The state of the art on food safety sensors will be summarized in this review including optical, electrochemical, and other sensor-based detection methods such as magnetoelastic or mass-based sensors.

Rapid Detection and Identification of Vancomycin-Sensitive Bacteria Using an Electrochemical Apta-Sensor

In order to combat the complex and diverse infections caused by bacteria, it is essential to develop efficient diagnostic tools. Current techniques for bacterial detection rely on laborious multistep procedures, with high costs and extended time of analysis. To overcome these limitations, we propose here a novel portable electrochemical biosensor for the rapid detection and identification of Gram-positive bacteria that leverages the recognition capabilities of vancomycin and aptamers. A vancomycin-modified screen-printed carbon electrode was used to selectively capture Gram-positive bacteria susceptible to this antibiotic. Electrochemical impedance spectroscopy and scanning electron microscopy demonstrated that capture was achieved in 10 min, with a limit of detection of only 2 CFU/mL. We then tested the device's potential for aptamer-based bacterial identification using Staphylococcus aureus and Bacillus cereus as the test strains. Specifically, electrodes with captured bacteria were exposed to species-specific aptamers, and the resulting changes in current intensity were analyzed using differential pulse voltammetry. When used directly in untreated milk or serum, the system was able to successfully identify a small amount of S. aureus and B. cereus (100 CFU/mL) in less than 45 min. This novel biosensor has the potential to serve as an invaluable tool that could be used, even by inexperienced staff, in a broad range of settings including clinical diagnostics, food safety analysis, environmental monitoring, and security applications.

Protease detection in the biosensor era: A review

Proteases have been proposed as potential biomarkers for several pathological conditions including cancers, multiple sclerosis and cardiovascular diseases, due to their ability to break down the components of extracellular matrix and basement membrane. The development of protease biosensors opened up the possibility to investigate the proteolytic activity of dysregulated proteases with higher efficiency over the traditional detection assays due to their quick detection capability, high sensitivity and selectivity, simple instrumentation and cost-effective fabrication processes. In contrast to the recently published review papers that primarily focused on one specific class of proteases or one specific detection method, this review article presents different optical and electrochemical detection methods that can be used to design biosensors for all major protease families. The benefits and drawbacks of various transducer techniques integrated into protease biosensing platforms are analyzed and compared. The main focus is on activity-based biosensors that use peptides as biorecognition elements. The effects of nanomaterials on biosensor performance are also discussed. This review should help readers to select the biosensor that best fits their needs, and contribute to the further development of this research field. Protease biosensors may allow better comprehension of protease overexperession and potentially enable novel devices for point-of-care testing.

Biosensing Platform for the Detection of Biomarkers for ALI/ARDS in Bronchoalveolar Lavage Fluid of LPS Mice Model

Acute respiratory distress syndrome (ARDS) is a worldwide health concern. The pathophysiological features of ALI/ARDS include a pulmonary immunological response. The development of a rapid and low-cost biosensing platform for the detection of ARDS is urgently needed. In this study, we report the development of a paper-based multiplexed sensing platform to detect human NE, PR3 and MMP-2 proteases. Through monitoring the three proteases in infected mice after the intra-nasal administration of LPS, we showed that these proteases played an essential role in ALI/ARDS. The paper-based sensor utilized a colorimetric detection approach based on the cleavage of peptide-magnetic nanoparticle conjugates, which led to a change in the gold nanoparticle-modified paper sensor. The multiplexing of human NE, PR3 and MMP-2 proteases was tested and compared after 30 min, 2 h, 4 h and 24 h of LPS administration. The multiplexing platform of the three analytes led to relatively marked peptide cleavage occurring only after 30 min and 24 h. The results demonstrated that MMP-2, PR3 and human NE can provide a promising biosensing platform for ALI/ARDS in infected mice at different stages. MMP-2 was detected at all stages (30 min-24 h); however, the detection of human NE and PR3 can be useful for early- (30 min) and late-stage (24 h) detection of ALI/ARDS. Further studies are necessary to apply these potential diagnostic biosensing platforms to detect ARDS in patients.

Bioaffinity Nanoprobes for Foodborne Pathogen Sensing

Bioaffinity nanoprobes are a type of biosensor that utilize the specific binding properties of biological molecules, such as antibodies, enzymes, and nucleic acids, for the detection of foodborne pathogens. These probes serve as nanosensors and can provide highly specific and sensitive detection of pathogens in food samples, making them an attractive option for food safety testing. The advantages of bioaffinity nanoprobes include their ability to detect low levels of pathogens, rapid analysis time, and cost-effectiveness. However, limitations include the need for specialized equipment and the potential for cross-reactivity with other biological molecules. Current research efforts focus on optimizing the performance of bioaffinity probes and expanding their application in the food industry. This article discusses relevant analytical methods, such as surface plasmon resonance (SPR) analysis, Fluorescence Resonance Energy Transfer (FRET) measurements, circular dichroism, and flow cytometry, that are used to evaluate the efficacy of bioaffinity nanoprobes. Additionally, it discusses advances in the development and application of biosensors in monitoring foodborne pathogens.

Ultrasensitive visual detection of the food-borne pathogen via MOF encapsulated enzyme

Various methods have been made to achieve sensitive detection (10 CFU/mL) of Escherichia coli O157:H7 (E. coli) in real samples, however, they are complex, time-consuming, or instrument-dependent. Enzyme-catalyzed reactions are one of the most efficient methods to amplify signals for sensitive detection. ZIF-8 owning stability, porosity, and high specific area are suitable for embedding enzymes which can effectively protect enzyme activity and thus improve detection sensitivity. Herein, a simple visual assay of E. coli with the limits of detection of 1 CFU/mL was developed based on this stable enzyme-catalyzed amplified system. A microbial safety test of milk, orange juice, seawater, cosmetic, and hydrolyzed yeast protein, was successfully performed with the limits of detection of 10 CFU/mL by the naked eye. And this bioassay possessed high selectivity and stability making the developed detection method practically promising.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

Recent Advances in Microfluidics-Based Electrochemical Sensors for Foodborne Pathogen Detection

Using pathogen-infected food that can be unhygienic can result in severe diseases and an increase in mortality rate among humans. This may arise as a serious emergency problem if not appropriately restricted at this point of time. Thus, food science researchers are concerned with precaution, prevention, perception, and immunity to pathogenic bacteria. Expensive, elongated assessment time and the need for skilled personnel are some of the shortcomings of the existing conventional methods. Developing and investigating a rapid, low-cost, handy, miniature, and effective detection technology for pathogens is indispensable. In recent times, there has been a significant scope of interest for microfluidics-based three-electrode potentiostat sensing platforms, which have been extensively used for sustainable food safety exploration because of their progressively high selectivity and sensitivity. Meticulously, scholars have made noteworthy revolutions in signal enrichment tactics, measurable devices, and portable tools, which can be used as an allusion to food safety investigation. Additionally, a device for this purpose must incorporate simplistic working conditions, automation, and miniaturization. In order to meet the critical needs of food safety for on-site detection of pathogens, point-of-care testing (POCT) has to be introduced and integrated with microfluidic technology and electrochemical biosensors. This review critically discusses the recent literature, classification, difficulties, applications, and future directions of microfluidics-based electrochemical sensors for screening and detecting foodborne pathogens.

Fluorescent aptasensor for detection of live foodborne pathogens based on multicolor perovskite-quantum-dot-encoded DNA probes and dual-stirring-bar-assisted signal amplification

In this study, a fluorescent (FL) aptasensor was developed for on-site detection of live Salmonella typhimurium (S.T.) and Vibrio parahaemolyticus (V.P.). Complementary DNA (cDNA) of aptamer (Apt)-functionalized multicolor polyhedral oligomeric silsesquioxane-perovskite quantum dots (cDNA-POSS-PQDs) were used as encoded probes and combined with dual-stirring-bar-assisted signal amplification for pathogen quantification. In this system, bar 1 was labeled with the S.T. and V.P. Apts, and then bar 2 was functionalized with cDNA-POSS-PQDs. When S.T. and V.P. were introduced, pathogen-Apt complexes would form and be released into the supernatant from bar 1. Under agitation, the two complexes reached bar 2 and subsequently reacted with cDNA-POSS-PQDs, which were immobilized on MXene. Then, the encoded probes would be detached from bar 2 to generate FL signals in the supernatant. Notably, the pathogens can resume their free state and initiate next cycle. They swim between the two bars, and the FL signals can be gradually enhanced to maximum after several cycles. The FL signals from released encoded probes can be used to detect the analytes. In particular, live pathogens can be distinguished from dead ones by using an assay. The detection limits and linear range for S.T. and V.P. were 30 and 10 CFU/mL and 10²-10⁶ CFU/mL, respectively. Therefore, this assay has broad application potential for simultaneous on-site detection of various live pathogenic bacteria in water.

Naked-eye detection of Staphylococcus aureus in powdered milk and infant formula using gold nanoparticles

Nonspecific binding of proteins from complex food matrices is a significant challenge associated with a biosensor using gold nanoparticles (AuNPs). To overcome this, we developed an efficient EDTA chelating treatment to denature milk proteins and prevent their adsorption on AuNPs. The use of EDTA to solubilize proteins enabled a sensitive label-free apta-sensor platform for colorimetric detection of Staphylococcus aureus in milk and infant formula. In the assay, S. aureus depleted aptamers from the test solution, and the reduction of aptamers enabled aggregation of AuNPs upon salt addition, a process characterized by a color change from red to purple. Under optimized conditions, S. aureus could be visually detected within 30 min with the detection limit of 7.5 × 10⁴ CFU/mL and 8.4 × 10⁴ CFU/mL in milk and infant formula, respectively. The EDTA treatment provides new opportunities for monitoring milk contamination and may prove valuable for biosensor point-of-need applications.

Biosensors, modern technology for the detection of cancer-associated bacteria

Cancer is undoubtedly one of the major human challenges worldwide. A number of pathogenic bacteria are deemed to be potentially associated with the disease. Accordingly, accurate and specific identification of cancer-associated bacteria can play an important role in cancer control and prevention. A variety of conventional methods such as culture, serology, and molecular-based methods as well as PCR and real-time PCR have been adopted to identify bacteria. However, supply costs, machinery fees, training expenses, consuming time, and the need for advanced equipment are the main problems with the old methods. As a result, advanced and modern techniques are being developed to overcome the disadvantages of conventional methods. Biosensor technology is one of the innovative methods that has been the focus of researchers due to its numerous advantages. The main purpose of this study is to provide an overview of the latest developed biosensors for recognizing the paramount cancer-associated bacteria.

Bi-ECDAQ: An electrochemical dual-immuno-biosensor accompanied by a customized bi-potentiostat for clinical detection of SARS-CoV-2 Nucleocapsid proteins

Multiplex electrochemical biosensors have been used for eliminating the matrix effect in complex bodily fluids or enabling the detection of two or more bioanalytes, overall resulting in more sensitive assays and accurate diagnostics. Many electrochemical biosensors lack reliable and low-cost multiplexing to meet the requirements of point-of-care detection due to either limited functional biosensors for multi-electrode detection or incompatible readout systems. We developed a new dual electrochemical biosensing unit accompanied by a customized potentiostat to address the unmet need for point-of-care multi-electrode electrochemical biosensing. The two-working electrode system was developed using screen-printing of a carboxyl-rich nanomaterial containing ink, with both working electrodes offering active sites for recognition of bioanalytes. The low-cost bi-potentiostat system (∼$80) was developed and customized specifically to the bi-electrode design and used for rapid, repeatable, and accurate measurement of electrochemical impedance spectroscopy signals from the dual biosensor. This binary electrochemical data acquisition (Bi-ECDAQ) system accurately and selectively detected SARS-CoV-2 Nucleocapsid protein (N-protein) in both spiked samples and clinical nasopharyngeal swab samples of COVID-19 patients within 30 min. The two working electrodes offered the limit of detection of 116 fg/mL and 150 fg/mL, respectively, with the dynamic detection range of 1-10,000 pg/mL and the sensitivity range of 2744-2936 Ω mL/pg.mm² for the detection of N-protein. The potentiostat performed comparable or better than commercial Autolab potentiostats while it is significantly lower cost. The open-source Bi-ECDAQ presents a customizable and flexible approach towards addressing the need for rapid and accurate point-of-care electrochemical biosensors for the rapid detection of various diseases.

Review of Label-Free Monitoring of Bacteria: From Challenging Practical Applications to Basic Research Perspectives

Novel biosensors already provide a fast way to detect the adhesion of whole bacteria (or parts of them), biofilm formation, and the effect of antibiotics. Moreover, the detection sensitivities of recent sensor technologies are large enough to investigate molecular-scale biological processes. Usually, these measurements can be performed in real time without using labeling. Despite these excellent capabilities summarized in the present work, the application of novel, label-free sensor technologies in basic biological research is still rare; the literature is dominated by heuristic work, mostly monitoring the presence and amount of a given analyte. The aims of this review are (i) to give an overview of the present status of label-free biosensors in bacteria monitoring, and (ii) to summarize potential novel directions with biological relevancies to initiate future development. Optical, mechanical, and electrical sensing technologies are all discussed with their detailed capabilities in bacteria monitoring. In order to review potential future applications of the outlined techniques in bacteria research, we summarize the most important kinetic processes relevant to the adhesion and survival of bacterial cells. These processes are potential targets of kinetic investigations employing modern label-free technologies in order to reveal new fundamental aspects. Resistance to antibacterials and to other antimicrobial agents, the most important biological mechanisms in bacterial adhesion and strategies to control adhesion, as well as bacteria-mammalian host cell interactions are all discussed with key relevancies to the future development and applications of biosensors.

A novel electrochemical sandwich-like immunosensor based on carboxyl Ti3C2Tx MXene and rhodamine b/gold/reduced graphene oxide for Listeria monocytogenes

Listeria monocytogenes (LM) is one of the most common food-borne pathogens and can induce a series of diseases with a high mortality rate to humans; hence, it is very necessary to develop a highly sensitive method for LM detection. Based on this need, a new sandwich-like electrochemical immunosensing platform was developed herein by preparing carboxyl Ti₃C₂T_x MXene (C-Ti₃C₂T_x MXene) as the sensing platform and rhodamine b/gold/reduced graphene oxide (RhB/Au/RGO) as the signal amplifier. The high conductivity and large surface area of C-Ti₃C₂T_x MXene make it a desirable nanomaterial to fix the primary antibody of LM (PAb), while the prepared Au/RGO/RhB nanohybrid is dedicated to assembling the secondary antibody (SAb) of LM, offering an amplified response signal. Through the use of RhB molecule as the signal probe, the experiments showed that the peak currents of RhB increase along with an increase in the concentration of LM from 10 to 10⁵ CFU mL^-1, and an extremely low limit of detection (2 CFU mL^-1) was obtained on the basis of the proposed immunosensing platform after optimizing various conditions. Hence, it is confirmed that the developed sandwich-like immunosensor based on C-Ti₃C₂T_x MXene and RhB/Au/Gr has great application in the detection of LM and other analytes.

Double-Resonant Nanostructured Gold Surface for Multiplexed Detection

A novel double-resonant plasmonic substrate for fluorescence amplification in a chip-based apta-immunoassay is herein reported. The amplification mechanism relies on plasmon-enhanced fluorescence (PEF) effect. The substrate consists of an assembly of plasmon-coupled and plasmon-uncoupled gold nanoparticles (AuNPs) immobilized onto a glass slide. Plasmon-coupled AuNPs are hexagonally arranged along branch patterns whose resonance lies in the red band (∼675 nm). Plasmon-uncoupled AuNPs are sprinkled onto the substrate, and they exhibit a narrow resonance at 524 nm. Numerical simulations of the plasmonic response of the substrate through the finite-difference time-domain (FDTD) method reveal the presence of electromagnetic hot spots mainly confined in the interparticle junctions. In order to realize a PEF-based device for potential multiplexing applications, the plasmon resonances are coupled with the emission peak of 5-carboxyfluorescein (5-FAM) fluorophore and with the excitation/emission peaks of cyanine 5 (Cy5). The substrate is implemented in a malaria apta-immunoassay to detect Plasmodium falciparum lactate dehydrogenase (PfLDH) in human whole blood. Antibodies against Plasmodium biomarkers constitute the capture layer, whereas fluorescently labeled aptamers recognizing PfLDH are adopted as the top layer. The fluorescence emitted by 5-FAM and Cy5 fluorophores are linearly correlated (logarithm scale) to the PfLDH concentration over five decades. The limits of detection are 50 pM (1.6 ng/mL) with the 5-FAM probe and 260 fM (8.6 pg./mL) with the Cy5 probe. No sample preconcentration and complex pretreatments are required. Average fluorescence amplifications of 160 and 4500 are measured in the 5-FAM and Cy5 channel, respectively. These results are reasonably consistent with those worked out by FDTD simulations. The implementation of the proposed approach in multiwell-plate-based bioassays would lead to either signal redundancy (two dyes for a single analyte) or to a simultaneous detection of two analytes by different dyes, the latter being a key step toward high-throughput analysis.

Electrochemical nanobiosensors equipped with peptides: a review

Recent research in the field of electrochemical biosensors equipped with peptides and nanomaterials have been categorized, reviewed, and critically analyzed. Indeed, using these innovative biosensors can revolutionize biomedical diagnostics in the future. Saving lives, time, and money in this field will be considered as some main benefits of this type of diagnosis. Here, these biosensors have been categorized and evaluated in four main sections. In the first section, the focus is on investigating the types of electrochemical peptide-based nanobiosensors applied to detect pathogenic microorganisms, microbial toxins, and viruses. In the second section, due to the importance of rapid diagnosis and prognosis of various cancers, the electrochemical peptide-based nanobiosensors designed to detect cancer biomarkers have been reviewed and analyzed. In the third section, the electrochemical peptide-based nanobiosensors, which were applied to detect the essential and effective biomolecules in the various diseases, and health control, including enzymes, hormones, biomarkers, and other biomolecules, have been considered. Finally, using a comprehensive analysis, all the used elements in these biosensors have been presented as conceptual diagrams that can effectively guide researchers in future developments. The essential factors in evaluating and analyzing these electrochemical peptide-based nanobiosensors such as analyte, peptide sequence, functional groups interacted between the peptide sequences and other biosensing components, the applied nanomaterials, diagnostic techniques, detection range, and limit of detection have also been included. Other analyzable items such as the type of used redox marker and the location of the peptide sequence against the signal transducer were also considered.

Diagnostic biosensors for coronaviruses and recent developments

Coronaviruses are well known airborne viruses that infect humans, other mammals, and birds. COVID-19 is the disease caused by the last emerging type of corona viruses; SARS-CoV-2 which resulted in the ongoing pandemic. Since its first identification, SARS-CoV-2 has spread globally causing significant morbidity and mortality. Fast and reliable diagnostic methods are crucial to control the virus outbreak. In this chapter, we summarize the traditional methods used to detect corona viruses. Various biosensors used for the detection of the virus antibodies and antigens were briefly discussed. Different biosensing approaches for the detection of corona viruses were presented with special emphasis on the reported biosensors for the detection of SARS-CoV-2. Major advancements in the biosensors area for corona viruses such as the use of cotton, magnetic nanoparticles, graphene, gold nanoparticles, and portable devices are highlighted. The challenges and future perspectives in the biosensors for the detection of corona viruses are discussed.

Recent advances in electrochemical strategies for bacteria detection

Introduction: Bacterial infections have always been a major threat to public health and humans' life, and fast detection of bacteria in various samples is significant to provide early and effective treatments. Cell-culture protocols, as well-established methods, involve labor-intensive and complicated preparation steps. For overcoming this drawback, electrochemical methods may provide promising alternative tools for fast and reliable detection of bacterial infections. Methods: Therefore, this review study was done to present an overview of different electrochemical strategy based on recognition elements for detection of bacteria in the studies published during 2015-2020. For this purpose, many references in the field were reviewed, and the review covered several issues, including (a) enzymes, (b) receptors, (c) antimicrobial peptides, (d) lectins, (e) redox-active metabolites, (f) aptamer, (g) bacteriophage, (h) antibody, and (i) molecularly imprinted polymers. Results: Different analytical methods have developed are used to bacteria detection. However, most of these methods are highly time, and cost consuming, requiring trained personnel to perform the analysis. Among of these methods, electrochemical based methods are well accepted powerful tools for the detection of various analytes due to the inherent properties. Electrochemical sensors with different recognition elements can be used to design diagnostic system for bacterial infections. Recent studies have shown that electrochemical assay can provide promising reliable method for detection of bacteria. Conclusion: In general, the field of bacterial detection by electrochemical sensors is continuously growing. It is believed that this field will focus on portable devices for detection of bacteria based on electrochemical methods. Development of these devices requires close collaboration of various disciplines, such as biology, electrochemistry, and biomaterial engineering.

Highly Sensitive Electrochemical Immunosensing for Listeria Monocytogenes Based on 3,4,9,10-Perylene Tetracarboxylic Acid/Graphene Ribbons as a Sensing Platform and Ferrocene/Gold Nanoparticles as an Amplifier

As a gram-positive foodborne pathogen, Listeria monocytogenes (LM) can cause many serious diseases to the human health coupled with high mortality rates; thus, constructing an effective method to detect LM is of great significance. Herein, a novel sandwich-type electrochemical immunosensor is proposed for LM by introducing 3,4,9,10-perylene tetracarboxylic acid/graphene ribbons (PTCA/GNR) nanohybrids as a sensing platform and ferrocene/gold nanoparticles (Fc/Au NPs) as a signal amplifier. The high conductivity and large surface area of GNR can increase the immobilizing amount of the primary antibody (PAb) and enhance the electron transport rate, while Au NPs can carry secondary antibodies (SAb) and Fc derivative (Fc-SH) to form a SAb-Au NPs-Fc signal amplifier. Through using Fc molecules as a signal probe, its peak current can appear and increase varied from the LM concentrations; hence, a highly sensitive sandwich-type immunosensor was constructed wide linear range from 10 to 2 × 10⁴-CFU mL^-1 and low limit of detection of low to 6 CFU mL^-1. Furthermore, the specificity of the immunosensor was also studied and a satisfactory result was obtained.

Simple electrochemical detection of Listeria monocytogenes based on a surface-imprinted polymer-modified electrode

Listeria monocytogenes (LM) is a foodborne pathogen, and it can pose a risk of serious diseases to the human health. Hence, the development of an effective method for the detection of LM is very important. In this study, by selecting LM as the template and 3-thiopheneacetic acid as the functional monomer, an LM-imprinted polymer (LIP)-based sensor was proposed for the first time to detect LM by electropolymerizing TPA on the glassy carbon electrode (GCE) surface in the presence of LM. After the removal of the LM template from the electrode surface, the obtained sensor was denoted as LIP/GCE, which could effectively recognize and capture LM cells. By using [Fe(CN)₆]^4-/3- as the probe, its peak current at LIP/GCE could be restricted when the LM cells were captured into the imprinted cavity of LIP/GCE, and the current value decreased with an increase in the LM concentration. Serious conditions were optimized for achieving highly sensitive detection, and a low detection limit (6 CFU mL^-1) coupled with a wide linear range (10 to 10⁶ CFU mL^-1) was obtained for LM. Finally, the inter-electrode reproducibility, stability, selectivity, and applicability of LIP/GCE were also investigated, and the obtained results were acceptable.

Advances in Nanomaterials-Based Electrochemical Biosensors for Foodborne Pathogen Detection

Electrochemical biosensors utilizing nanomaterials have received widespread attention in pathogen detection and monitoring. Here, the potential of different nanomaterials and electrochemical technologies is reviewed for the development of novel diagnostic devices for the detection of foodborne pathogens and their biomarkers. The overview covers basic electrochemical methods and means for electrode functionalization, utilization of nanomaterials that include quantum dots, gold, silver and magnetic nanoparticles, carbon nanomaterials (carbon and graphene quantum dots, carbon nanotubes, graphene and reduced graphene oxide, graphene nanoplatelets, laser-induced graphene), metal oxides (nanoparticles, 2D and 3D nanostructures) and other 2D nanomaterials. Moreover, the current and future landscape of synergic effects of nanocomposites combining different nanomaterials is provided to illustrate how the limitations of traditional technologies can be overcome to design rapid, ultrasensitive, specific and affordable biosensors.

The Role of Peptides in the Design of Electrochemical Biosensors for Clinical Diagnostics

Peptides represent a promising class of biorecognition elements that can be coupled to electrochemical transducers. The benefits lie mainly in their stability and selectivity toward a target analyte. Furthermore, they can be synthesized rather easily and modified with specific functional groups, thus making them suitable for the development of novel architectures for biosensing platforms, as well as alternative labelling tools. Peptides have also been proposed as antibiofouling agents. Indeed, biofouling caused by the accumulation of biomolecules on electrode surfaces is one of the major issues and challenges to be addressed in the practical application of electrochemical biosensors. In this review, we summarise trends from the last three years in the design and development of electrochemical biosensors using synthetic peptides. The different roles of peptides in the design of electrochemical biosensors are described. The main procedures of selection and synthesis are discussed. Selected applications in clinical diagnostics are also described.

Voltammetric-based immunosensor for the detection of SARS-CoV-2 nucleocapsid antigen

Since the COVID-19 disease caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) was declared a pandemic, it has spread rapidly, causing one of the most serious outbreaks in the last century. Reliable and rapid diagnostic tests for COVID-19 are crucial to control and manage the outbreak. Here, a label-free square wave voltammetry-based biosensing platform for the detection of SARS-CoV-2 in nasopharyngeal samples is reported. The sensor was constructed on screen-printed carbon electrodes coated with gold nanoparticles. The electrodes were functionalized using 11-mercaptoundecanoic acid (MUA) which was used for the immobilization of an antibody against SARS-CoV-2 nucleocapsid protein (N protein). The binding of the immunosensor with the N protein caused a change in the electrochemical signal. The detection was realised by measuring the change in reduction peak current of a redox couple using square wave voltammetry at 0.04 V versus Ag ref. electrode on the immunosensor upon binding with the N protein. The electrochemical immunosensor showed high sensitivity with a linear range from 1.0 pg.mL⁻¹ to 100 ng.mL⁻¹ and a limit of detection of 0.4 pg.mL⁻¹ for the N protein in PBS buffer pH 7.4. Moreover, the immunosensor did not exhibit significant response with other viruses such as HCoV, MERS-CoV, Flu A and Flu B, indicating the high selectivity of the sensor for SARS-CoV-2. However, cross reactivity of the biosensor with SARS-CoV is indicated, which gives ability of the sensor to detect both SARS-CoV and SARS-CoV-2. The biosensor was successfully applied to detect the SARS-CoV-2 virus in clinical samples showing good correlation between the biosensor response and the RT-PCR cycle threshold values. We believe that the capability of miniaturization, low-cost and fast response of the proposed label-free electrochemical immunosensor will facilitate the point-of-care diagnosis of COVID 19 and help prevent further spread of infection.

A comprehensive review on the applications of nano-biosensor-based approaches for non-communicable and communicable disease detection

The outstretched applications of biosensors in diverse domains has become the reason for their attraction for scientific communities. Because they are analytical devices, they can detect both quantitative and qualitative biological components through the generation of detectable signals. In the recent past, biosensors witnessed significant changes and developments in their design as well as features. Nanotechnology has revolutionized sensing phenomena by increasing biodiagnostic capacity in terms of specificity, size, and cost, resulting in exceptional sensitivity and flexibility. The steep increase of non-communicable diseases across the world has emerged as a matter of concern. In parallel, the abrupt outbreak of communicable diseases poses a serious threat to mankind. For decreasing the morbidity and mortality associated with various communicable and non-communicable diseases, early detection and subsequent treatment are indispensable. Detection of different biological markers generates quantifiable signals that can be electrochemical, mass-based, optical, thermal, or piezoelectric. Speculating on the incumbent applicability and versatility of nano-biosensors in large disciplines, this review highlights different types of biosensors along with their components and detection mechanisms. Moreover, it deals with the current advancements made in biosensors and the applications of nano-biosensors in detection of various non-communicable and communicable diseases, as well as future prospects of nano-biosensors for diagnostics.

Electrochemical Biosensors in Food Safety: Challenges and Perspectives

Safety and quality are key issues for the food industry. Consequently, there is growing demand to preserve the food chain and products against substances toxic, harmful to human health, such as contaminants, allergens, toxins, or pathogens. For this reason, it is mandatory to develop highly sensitive, reliable, rapid, and cost-effective sensing systems/devices, such as electrochemical sensors/biosensors. Generally, conventional techniques are limited by long analyses, expensive and complex procedures, and skilled personnel. Therefore, developing performant electrochemical biosensors can significantly support the screening of food chains and products. Here, we report some of the recent developments in this area and analyze the contributions produced by electrochemical biosensors in food screening and their challenges.

Modernization of Control of Pathogenic Micro-Organisms in the Food-Chain Requires a Durable Role for Immunoaffinity-Based Detection Methodology-A Review

Food microbiology is deluged by a vastly growing plethora of analytical methods. This review endeavors to color the context into which methodology has to fit and underlines the importance of sampling and sample treatment. The context is that the highest risk of food contamination is through the animal and human fecal route with a majority of foodborne infections originating from sources in mass and domestic kitchens at the end of the food-chain. Containment requires easy-to-use, failsafe, single-use tests giving an overall risk score in situ. Conversely, progressive food-safety systems are relying increasingly on early assessment of batches and groups involving risk-based sampling, monitoring environment and herd/flock health status, and (historic) food-chain information. Accordingly, responsible field laboratories prefer specificity, multi-analyte, and high-throughput procedures. Under certain etiological and epidemiological circumstances, indirect antigen immunoaffinity assays outperform the diagnostic sensitivity and diagnostic specificity of e.g., nucleic acid sequence-based assays. The current bulk of testing involves therefore ante- and post-mortem probing of humoral response to several pathogens. In this review, the inclusion of immunoglobulins against additional invasive micro-organisms indicating the level of hygiene and ergo public health risks in tests is advocated. Immunomagnetic separation, immunochromatography, immunosensor, microsphere array, lab-on-a-chip/disc platforms increasingly in combination with nanotechnologies, are discussed. The heuristic development of portable and ambulant microfluidic devices is intriguing and promising. Tant pis, many new platforms seem unattainable as the industry standard. Comparability of results with those of reference methods hinders the implementation of new technologies. Whatever the scientific and technological excellence and incentives, the decision-maker determines this implementation after weighing mainly costs and business risks.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Peptide-based electrochemical biosensors utilized for protein detection

Proteins are generally detected as biomarkers for tracing or determining various disorders in organisms. Biomarker proteins can be tracked in samples with various origins and in different concentrations, revealing whether an organism is in a healthy or unhealthy state. In regard to detection, electrochemical biosensors are a potential fusion of electronics, chemistry, and biology, allowing for fast and early point-of-care detection from a biological sample with the advantages of high sensitivity, simple construction, and easy operation. Peptides present a promising approach as a biorecognition element when connected with electrochemical biosensors. The benefits of short peptides lie mainly in their good stability and selective affinity to a target analyte. Therefore, peptide-based electrochemical biosensors (PBEBs) represent an alternative approach for the detection of different protein biomarkers. This review provides a summary of the past decade of recently proposed PBEBs designed for protein detection, dividing them according to different protein types: (i) enzyme detection, including proteases and kinases; (ii) antibody detection; and (iii) other protein detection. According to these protein types, different sensing mechanisms are discussed, such as the peptide cleavage by a proteases, phosphorylation by kinases, presence of antibodies, and exploiting of affinities; furthermore, measurements are obtained by different electrochemical methods. A discussion and comparison of various constructions, modifications, immobilization strategies and different sensing techniques in terms of high sensitivity, selectivity, repeatability, and potential for practical application are presented.

Development of a Low-Cost Cotton-Tipped Electrochemical Immunosensor for the Detection of SARS-CoV-2

Collection of nasopharyngeal samples using swabs followed by the transfer of the virus into a solution and an RNA extraction step to perform reverse transcription polymerase chain reaction (PCR) is the primary method currently used for the diagnosis of COVID-19. However, the need for several reagents and steps and the high cost of PCR hinder its worldwide implementation to contain the outbreak. Here, we report a cotton-tipped electrochemical immunosensor for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus antigen. Unlike the reported approaches, we integrated the sample collection and detection tools into a single platform by coating screen-printed electrodes with absorbing cotton padding. The immunosensor was fabricated by immobilizing the virus nucleocapsid (N) protein on carbon nanofiber-modified screen-printed electrodes which were functionalized by diazonium electrografting. The detection of the virus antigen was achieved via swabbing followed by competitive assay using a fixed amount of N protein antibody in the solution. A square wave voltammetric technique was used for the detection. The limit of detection for our electrochemical biosensor was 0.8 pg/mL for SARS-CoV-2, indicating very good sensitivity for the sensor. The biosensor did not show significant cross-reactivity with other virus antigens such as influenza A and HCoV, indicating high selectivity of the method. Moreover, the biosensor was successfully applied for the detection of the virus antigen in spiked nasal samples showing excellent recovery percentages. Thus, our electrochemical immunosensor is a promising diagnostic tool for the direct rapid detection of the COVID-19 virus that requires no sample transfer or pretreatment.

A critical review on quantum dots: From synthesis toward applications in electrochemical biosensors for determination of disease-related biomolecules

Fluorescent quantum dots (QDs), defined by a diameter size of <10 nm, have been the core concept of nanoscience and nanotechnology since their inception. QDs possess many unique structural, electrochemical and photochemical properties that render them a promising platform for sensing applications. These nanomaterials can greatly enhance the analytical performances of biosensors, namely detection limit, sensitivity and selectivity. QDs are being developed not only because of their ability for signal enhancement but also because of their high capacity for fuctionalization with bioreceptors. In this review, we summarize a basic knowledge of QDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into the sensing field. Due to the nature of QDs, especially their ability to combine nanotechnology and biotechnology, they possess the potential to open a novel paradigm on early diagnosis of diseases using the electrochemical biosensors. Therefore, we try to give a comprehensive view of the role of these zero-dimensional (0D) nanomaterials in the designing electrochemical sensors for determination of disease-related biomolecules, including tumor markers, inflammatory biomarkers, depression markers and archetypal biomarker in diabetes diagnosis. Considering the high potential of QDs for the electrochemistry-based biosensing strategies, the authors suggest that more research is needed on understanding their electronic properties and why synthesis and surface modification methods can affect these properties.