Antibiotic-enzyme-inorganic nanoflowers based immunoassay for the ultrasensitive detection of Staphylococcus aureus

Curcumin - a natural colorant-based pH indicator for molecular diagnostics

Loop-mediated isothermal amplification (LAMP) provides highly selective and sensitive DNA amplification and generates hydrogen ions as a byproduct under weakly buffered conditions, causing the solutions' pH to decrease from the initial basic to an acidic environment. This distinctive feature allows the color of the amplified DNA solution to change readily when suitable pH indicators are employed. In this study, curcumin, a biodegradable, non-toxic, and natural colorant, was used as a pH indicator to visually identify LAMP-amplified Staphylococcus aureus (S. aureus) and Streptococcus pneumoniae (S. pneumoniae). Curcumin (10 mM) displayed a unique color difference between negative (red) and positive (yellow) samples, and the detection process was completed within 30 s, demonstrating the effectiveness of using curcumin for on-site diagnostics. Under optimum conditions, curcumin enabled S. aureus and S. pneumoniae detection as low as 10 fg μL-1 and 1 pg μL-1, respectively, due to its unique halochromic properties. Owing to its adaptability, ease of use, and rapid visual detection, the introduced colorimetric pH-based LAMP method can be employed as a practical alternative to conventional colorimetry for infectious pathogen identification in both laboratory and field settings.

Top-Down Computational Design of Molecule Recognition Peptides (MRPs) for Enzyme-Peptide Self-Assembly and Chemiluminescent Biosensing

The recognition of small molecules plays a crucial role in disease diagnosis, environmental assessment, and food safety. Currently, their recognition elements predominantly rely on antibodies and aptamers while suffering from a limitation of the complex screening process due to the low immunogenicity of small molecules. Herein, we present a top-down computational design strategy for molecule recognition peptides (MRPs) for enzyme-peptide self-assembly and chemiluminescence biosensing. Taking ochratoxin A (OTA) as an illustrative example, human serum albumin (HSA) was selected as the parental protein due to its high affinity for OTA binding. Through iterative computational simulations involving the binding domain of the HSA-OTA complex, our strategy identified a specific 15-mer MRP (RLKCASLKFGERAFK), which possesses excellent binding affinity (38.02 ± 1.24 nM) against OTA. Molecular dynamics simulations revealed that the 15-mer MRP unfolds into a flexible short chain with high affinity for OTA, but exhibits weak or no binding affinity with five structurally similar mycotoxins. Furthermore, we developed a novel enzyme-peptide self-assembly approach mediated by calcium(II) to obtain nanoflowers, which integrates both the recognition element (MRP) and the signal translator (enzyme) for chemiluminescence biosensing. The assembled nanoflowers allow MRPs to be directly utilized as a tracer for OTA biosensing without labeling or secondary antibodies. This computational-to-application approach offers a new route for small-molecule recognition.

Rapid Dynamic Surface-Enhanced Raman Spectroscopy Detection of Amoxicillin-Mediated Morphological Changes in a Pathogen for Diagnosis of Clinical Urine Samples

The swift and stable detection of pathogens in urine samples holds significant implications for the immediate clinical diagnosis and treatment of urinary tract infections (UTIs). In this study, we propose a detection strategy utilizing a hybrid substrate composed of graphene oxide (GO) and silver nanoparticles (Ag NPs) for the detection of pathogens subjected to amoxicillin-mediated (amo-mediated) treatment. This strategy employs dynamic surface-enhanced Raman spectroscopy (D-SERS) for stable and rapid detection, capturing signal variations induced by amo-mediated changes in pathogen morphology. During the 5 min D-SERS detection time window, stable SERS signals were detected for three types of pathogens and four types of pathogens were successfully distinguished using principal component analysis (PCA). In comparison to conventional nanosubstrates, the GO/Ag NP hybrid substrate exhibits outstanding stability and enhancement effects. This approach enables the dual detection of the pathogen cell structure and metabolites, facilitating specific identification of pathogens in the urinary tract, with a detection limit for Escherichia coli reaching 1 × 104 colony-forming units (CFU)/mL, meeting the clinical microbiology laboratory diagnostic standards for UTIs (105 CFU/mL). Testing of 188 clinically collected urine samples using this strategy yielded a sensitivity (SENS) of 86.4% and a specificity (SPC) of 89.7%. This introduces a novel method for diagnosing UTIs, offering broad applications in the field of clinical pathogen detection.

A Clickase-Mediated Immunoassay Based on Nanopore and Bionic Signal Labels for Ultrasensitive, Portable, and On-Site Detection of Ricin

It is of particular importance to develop an effective method that possesses several merits simultaneously of rapid, ultrasensitive, portable, and on-site detection potential for food safety detection. Herein, we propose a clickase-mediated immunoassay based on nanopore and bionic signal labels for the detection of ricin. The introduction of Cu/Cys clickase and nanopore simultaneously effectively addressed the inherent limitations of natural enzymes and colorimetric signal output, respectively. Using this method, bionic signal labels can be easily formed through DNA and Gram-positive bacterial cell wall terminal peptide fragments (labeled by alkynyl and azide, respectively) and vancomycin. Translocation of the D-P@vancomycin through the nanopore generated highly specific oscillation current traces. This method showed a great on-site detection potential and superior analytical performance owing to the combination of the specificity of antibodies, high CuAAC click reaction catalytic efficiency of clickase, ultrasensitivity of the nanopore, and high signal resolution of D-P@vancomycin. Moreover, the practical applicability of the established method was also verified, achieving a limit of detection (LOD) down to 200.9 ag/mL with a wide linear relationship under the optimized conditions. In conclusion, this method is promising for rapid, portable, ultrasensitive, and on-site food safety detection.

Hook-Like DNAzyme-Activated Autocatalytic Biosensor for the Universal Detection of Pathogenic Bacteria

DNAzyme-based assays have found extensive utility in pathogenic bacteria detection but often suffer from limited sensitivity and specificity. The integration of a signal amplification strategy could address this challenge, while the existing combination methods require extensive modification to accommodate various DNAzymes, limiting the wide-spectrum bacteria detection. We introduced a novel hook-like DNAzyme-activated autocatalytic nucleic acid circuit for universal pathogenic bacteria detection. The hook-like connector DNA was employed to seamlessly integrate the recognition element DNAzyme with the isothermal enzyme-free autocatalytic hybridization chain reaction and catalytic hairpin assembly for robust exponential signal amplification. This innovative autocatalytic circuit substantially amplifies the output signals from the DNAzyme recognition module, effectively overcoming DNAzyme's inherent sensitivity constraints in pathogen identification. The biosensor exhibits a strong linear response within a range of 1.5 × 103 to 3.7 × 107 CFU/mL, achieving a detection limit of 1.3 × 103 CFU/mL. Noted that the sensor's adaptability as a universal detection platform is established by simply modifying the hook-like connector module, enabling the detection of various pathogenic bacteria of considerable public health importance reported by the World Health Organization, including Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Salmonella typhimurium. Additionally, the specificity of DNAzyme in bacterial detection is markedly improved due to the signal amplification process of the autocatalytic circuit. This hook-like DNAzyme-activated autocatalytic platform presents a versatile, sensitive, and specific approach for pathogenic bacteria detection, promising to significantly expand the applications of DNAzyme in bacteria detection.

Nanotopology-Enabled On-Site Pathogen Detection for Managing Atopic Dermatitis

Atopic dermatitis (AD), a prevalent skin condition often complicated by microbial infection, poses a significant challenge in identifying the responsible pathogen for its effective management. However, a reliable, safe tool for pinpointing the source of these infections remains elusive. In this study, a novel on-site pathogen detection that combines chemically functionalized nanotopology with genetic analysis is proposed to capture and analyze pathogens closely associated with severe atopic dermatitis. The chemically functionalized nanotopology features a 3D hierarchical nanopillar array (HNA) with a functional polymer coating, tailored to isolate target pathogens from infected skin. This innovative nanotopology demonstrates superior pathogenic capture efficiency, favorable entrapment patterns, and non-cytotoxicity. An HNA-assembled stick is utilized to directly retrieve bacteria from infected skin samples, followed by extraction-free quantitative loop-mediated isothermal amplification (direct qLAMP) for validation. To mimic human skin conditions, porcine skin is employed to successfully capture Staphylococcus aureus, a common bacterium exacerbating AD cases. The on-site detection method exhibits an impressive detection limit of 103 cells mL-1. The HNA-assembled stick represents a promising tool for on-site detection of bacteria associated with atopic dermatitis. This innovative approach enables to deepen the understanding of AD pathogenesis and open avenues for more effective management strategies for chronic skin conditions.

Applying a sandwich-like strategy for dual 'light up' capture and eradication of Staphylococcus aureus using magnetically functionalized materials

In this study, we proposed an innovative application of porcine immunoglobulin G (IgG)-functionalized Fe3O4 (IgG-Fe3O4) specifically designed to target and capture Staphylococcus aureus (S. aureus). In addition, aminophenylboronic acid-modified tetraphenylethylene nanoparticles (APBA-TPE NPs) were utilized, establishing a sandwich-type dual recognition system via interactions with the bacteria's extracellular glycolipids. This approach enables highly sensitive and precise detection of bacterial presence, with a limit of detection (LOD) reaching down to 5.0 CFU/mL. Specifically, the prepared APBA-TPE NPs achieved 99.99% bacterial inactivation within 60 min at a concentration of 200 µg/mL. The results showed that APBA-TPE NPs possess a remarkable capacity for reactive oxygen species (ROS) production, which could attack the bacterial cell membrane, leading to bacterial lysis and content leakage, and ultimately to bacterial death. Furthermore, the material still showed good recoveries ranging from 88.5% to 93.5% in actual water samples, as well as a favorable sterilizing effect of killing all microorganisms for 60 min. This research provides new strategies and insights into the construction of methods for the specific capture, detection, and inactivation of S. aureus.

Specific separation and sensitive detection of foodborne pathogens by phage-derived bacterial-binding protein-nano magnetic beads coupled with smartphone-assisted paper sensor

Foodborne pathogen infection poses a significant threat to public health and is considered as one of the most serious hazards in global food safety. Herein, a sensitive and efficient method for on-site monitoring of foodborne pathogens was developed by using a smartphone-assisted paper-sensor combined with phage-derived bacterial-binding proteins-nano magnetic beads (PBPs-MBs). PBPs including tail fiber protein (TFP:gp13), cell-wall binding domain (CBD) of endolysin and tailspike protein (TSP) coated on the surface of MBs were applied for rapid separation and enrichment of targeted bacteria (Escherichia coli O157:H7, Staphylococcus aureus and Salmonella typhimurium, respectively) from food samples in 20 min before detection on paper-based sensors. The paper-based sensor was loaded with the lytic agent (polymyxin B) to induce bacterial lysis and release specific endogenous enzymes. Subsequently, three distinct chromogenic substrates were hydrolyzed by their corresponding enzymes, resulting in characteristic color changes on the paper, respectively. In addition, a smartphone APP for red-green-blue (RGB) color analysis of paper was able to directly detect three foodborne pathogens. As a result, the limit of detection (LOD) values for three foodborne pathogens were found to be 2.44 × 102, 2.68 × 104 and 4.62 × 103 CFU/mL, respectively, which were much lower than other studies (106-108 CFU/mL) based on enzymes. Moreover, the feasibility of this approach was further assessed through the successful detection of targeted bacteria in real samples with satisfactory recovery rates. In conclusion, this smartphone-assisted biosensor offers promising application potential for point-of-care testing (POCT) of foodborne pathogens in resource-scarce areas.

Nanomaterial-based biosensors for the detection of foodborne bacteria: a review

Ensuring food safety is a critical concern for the development and well-being of humanity, as foodborne illnesses caused by foodborne bacteria have increasingly become a major public health concern worldwide. Traditional food safety monitoring systems are expensive and time-consuming, relying heavily on specialized equipment and operations. Therefore, there is an urgent need to develop low-cost, user-friendly and highly sensitive biosensors for detecting foodborne bacteria. In recent years, the combination of nanomaterials with optical biosensors has provided a prospective future platform for the detection of foodborne bacteria. By harnessing the unique properties of nanomaterials, such as their high surface area-to-volume ratio and exceptional sensitivity, in tandem with the precision of optical biosensing techniques, a new prospect has opened up for the rapid and accurate identification of potential bacterial contaminants in food. This review focuses on recent advances and new trends of nanomaterial-based biosensors for the detection of foodborne pathogens, which mainly include noble metal nanoparticles (NMPs), metal organic frameworks (MOFs), graphene nanomaterials, quantum dot (QD) nanomaterials, upconversion fluorescent nanomaterials (UCNPs) and carbon dots (CDs). Additionally, we summarized the research progress of color indicators, nanozymes, natural enzyme vectors and fluorescent dye biosensors, focusing on the advantages and disadvantages of nanomaterial-based biosensors and their development prospects. This review provides an outlook on future technological directions and potential applications to help identify the most promising areas of development in this field.

Dual-Modal Biosensor for Staphylococcus aureus Detection Based on a Porphyrin-Based Porous Organic Polymer FePor-TPA with Excellent Peroxidase-like, Catalase-like, and Photoelectrochemical Properties

Bacterial infections seriously harm human health and cause many severe diseases, which triggered urgent demands to exploit specific and sensitive biosensor strategies for Staphylococcus aureus detection. Here, a colorimetric and photoelectrochemical dual-mode biosensor for S. aureus assay based on FePor-TPA was constructed. 2D FePor-TPA thin film and its bulk powder (FePor-TPA) were synthesized by in situ growth on ITO and a solvothermal condition, respectively, both of which exhibited excellent peroxidase-like and catalase-like activity, originating from their metalloporphyrin linkers. Benefiting from the in situ growth on ITO electrodes, the 2D FePor-TPA thin film also possessed a more ordered stacking mode and in turn exhibited good electrical conductivity, stable initial photocurrent, and high sensitivity to O2. As for bulk FePor-TPA, its porous structure and high specific surface area make it a possible scaffold to load an amount of AuNPs, the rabbit anti-Staphylococcus aureus Rosenbach tropina antibody (Ab2), and GOx for constructing the signal probe (GOx/Ab2@Au@FePor-TPA) and realizing catalytic amplification. With these satisfactory features in mind, the 2D FePor-TPA thin film and its bulk powder (FePor-TPA) were utilized to construct a dual and signal-on bioplatform for sensitively and selectively detecting S. aureus, which, as far as we know, has not been reported.