Dual enzyme induced colorimetric sensor for simultaneous identifying multiple pathogens

Starch-KI test strip and solution colorimetry for dual-mode point-of-care testing (POCT) of live Staphylococcus aureus based on the activity of lysed catalase

Staphylococcus aureus (S. aureus), a ubiquitous foodborne pathogenic bacterium, is prevalent in a wide array of food products and frequently implicated in food poisoning incidents, necessitating effective means for its real-time monitoring and rapid detection. In response to this need, this study introduces an innovative dual-mode point-of-care testing (POCT) approach for detecting live S. aureus, leveraging the catalase (CAT)-induced H2O2-mediated reaction. This method integrates a starch-KI paper test with solution colorimetry, offering a dual-modal detection system. The use of commercial starch-KI test strips stands out for its simplicity, cost-effectiveness, rapidness, and enhanced stability and repeatability in large-scale applications, as it requires no modifications or treatments. Furthermore, combining with the solution colorimetry, the dual signal outputs enable mutual correction, significantly boosting detection accuracy and minimizing both false positives and negatives. The starch-KI test strips provide swift visual results, allowing for immediate identification, while the enzyme cascade-based solution colorimetry offers quantitative analysis with impressive lower limits of detection (72 CFU mL-1 for solution colorimetry). These low detection thresholds demonstrate the system's high sensitivity and precision. This dual-modal platform enables real-time monitoring and early intervention in food systems, preventing food poisoning. Its practicality, low cost, and user-friendliness make it an appealing diagnostic tool for both industrial food processors and public health authorities, particularly in regions with limited resources. By addressing the critical need for accurate, rapid, and cost-effective S. aureus detection, this dual-modal platform could significantly contribute to enhancing food safety globally.

Faraday cage-type photocurrent polarity switching photoelectrochemical sensing platform for highly selective and sensitive detection of Vibrio parahaemolyticus

Highly selective and sensitive detection of foodborne pathogens is crucial for ensuring food safety. In this work, a photoelectrochemical (PEC) aptasensing platform was developed for the selective and sensitive detection of Vibrio parahaemolyticus (VP), adopting Faraday cage-type construction mode. When VP was present in the sample, the aptamer for VP (Apt) assembled on the Apt/Bi2S3/ITO electrode captured VP, which bound GO@Cu2O-Apt to the electrode surface. The graphene oxide (GO) in GO@Cu2O-Apt has a large surface area and good conductivity, on the surface of which a large amount of Cu2O that can switch the polarity of the Bi2S3 photocurrent was loaded, resulting in a highly selective and sensitive detection of VP with a detection limit of 1.0 CFU/mL. By adjusting the Apt, the platform can be used for the detection of other foodborne pathogens, offering broad application potential in foodborne pathogen detection.

Two birds with one stone: colorimetric and photothermal dual-mode biosensor based on CoOOH nanorings for detecting β-galactosidase activity and Escherichia coli

Pathogenic bacterial infections are a serious global public health threats, creating an urgent requirement for the rapid, sensitive, and reliable detection of bacteria. Herein, a multi-colorimetric and portable photothermal dual-mode biosensor with cross-references and self-calibration was established for the analysis of β-galactosidase (β-Gal) and Escherichia coli (E. coli).

Portable on-site colorimetric kit using stable gold nanorod powder for tracing hydrogen sulfide in typical environmental samples

On-site detection of hydrogen sulfide (H2S), a toxic byproduct of microbial decomposition, is essential for environmental surveys, sewage tracing, and occupational safety. While existing gold nanorods (Au NRs)-based colorimetric methods offer portability and sensitivity, their practicality is hindered by the instability of enzymes and colloidal nanoparticles. Herein, we present an enzyme-free, portable H2S detection device using Au NRs powder, ensuring highly sensitive and reliable colorimetric detection while enhancing long-term applicability. The sensing strategy involves two steps: H2S microextraction and colorimetric assay. First, H2S is accumulated into a NaOH aqueous drop from a complex sample matrix via headspace single-drop microextraction (HS-SDME) using sulfamic acid. In the colorimetric assay, dissolved H2S reduces KIO3 to I2 in glycine-HCl buffer (pH 2.6), which etches Au NRs in the presence of Br- and CTA+, causing a blue shift in the plasmon band with a distinct color change. This method achieves a visual detection limit of 0.05 µM, approximately 10 times lower than the Methylene Blue method. The use of HS-SDME ensures excellent selectivity against co-existing ions (≥10-fold) and small organic molecules (100-fold). Validation with real samples yielded recoveries of 92.40 %-109.51 %, demonstrating reliability in environmental monitoring and river pollution tracing. To simplify detection, we developed a liquid-free test kit containing an H2S microextraction tube (sulfamic acid powder), a colorimetric assay tube (Au NRs powder and solid buffer), and a portable heating device. This enzyme-free sensor ensures long-term stability and practicality, advancing Au NRs-based sensors for environmental monitoring.

Freeze-Thaw Imaging for Microorganism Classification Assisted with Artificial Intelligence

Fast and cost-effective microbial classification is crucial for clinical diagnosis, environmental monitoring, and food safety. However, traditional methods encounter challenges including intricate procedures, skilled personnel needs, and sophisticated instrumentations. Here, we propose a cost-effective microbe classification system, also termed freeze-thaw-induced floating pattern of AuNPs (FTFPA), coupled with artificial intelligence, which is capable of identifying microbes at a cost of $0.0023 per sample. Specifically, FTFPA utilizes AuNPs for coincubation with microbes, resulting in distinct patterns upon freeze-thawing due to their weak interaction. These patterns are digitized to train models that distinguish nine microbes in various tasks. The positive sample detection model achieved an F1 score of 0.976 (n = 194), while the multispecies classification task reached a macro F1 score of 0.859 (n = 1728). To address scalability and lightweight requirements across diverse classification scenarios, we categorized microbes based on species classification levels. The macro F1 score of the hierarchical model (n = 5184), order level model (n = 5184), Enterobacteriales level model (n = 2550), and Bacillales level model (n = 1974) was 0.854, 0.907, 0.958, and 0.843. In summary, our method is user-friendly, requiring only simple equipment, is easy to operate, and convenient, providing a platform for microbial identification.

Boronic acid-functionalized Fe3O4 nanoparticles for activity-preserved enrichment of low-abundance bacteria from real samples

Pathogenic bacterial infections represent a significant and ongoing threat to public health. The development of a sensitive, convenient, and accurate method for diagnosing pathogenic bacteria is a formidable challenge due to their low abundance in complex biological samples, especially in the early stages of diseases. In this study, a kind of phenylboronic acid-functionalized Fe3O4 nanoparticles (NPs), known as Fe3O4@poly(PEGDA-co-MAAPBA) NPs, was developed for effectively enriching low levels of pathogenic bacteria from complex samples and then diagnosing them through microbiological cultures. In this design, the resultant Fe3O4@poly(PEGDA-co-MAAPBA) NPs could recognize pathogenic bacteria because of the reversible reactions between the phenylboronic acid groups on the NPs and the cis-diol structures outside of the bacterial cells. By exploiting the magnetic properties of Fe3O4 NPs, bacteria were able to anchored onto the resulting NPs (NPs@bacteria) for easy enrichment. Utilizing microbiological culture techniques, successful cultivation of NPs@bacteria was achieved, demonstrating that bacterial activity remained unaffected during the enrichment process. The proposed method exhibited a limit of detection as low as 0.4 colony-forming units per milliliter. The Fe3O4@poly(PEGDA-co-MAAPBA) NPs were applied successfully for testing Staphylococcus aureus in urine samples which were typically considered to be free of bacterial contamination, indicating excellent selectivity and enrichment capability of the prepared NPs in complex samples. It suggests that the Fe3O4@poly(PEGDA-co-MAAPBA) NPs have the potential to become a powerful tool for early diagnosis of pathogenic bacteria in the clinic.

AIE multifunctional probe empowering colorimetric-fluorescence dual-mode biosensor for early diabetic screening

Diabetes mellitus (DM) is a serious chronic disease characterized by abnormally high blood glucose (Glu) levels, which can cause organ malfunction and metabolic disturbances. However, traditional biomarkers like Glu face limitations due to intraday fluctuations and inability to detect early stages of DM. To tackle these challenges, this study has introduced a colorimetric-fluorescence dual-mode biosensor utilizing α-glucosidase (α-GAA), which enables early diabetes screening without being influenced by physiological fluctuations in blood glucose levels. Specifically, chitosan-modified copper nanoclusters (Cu NC@CS-Ce3+: AP-CuCC) with exceptional peroxidase (POD) activity and Ce3+-induced aggregate-induced luminescence (AIE) properties have been synthesized. The targeted hydrolysis of the α-GAA substrate, 4-nitrophenyl-α-D-glucopyranoside (pNGP), results in the formation of p-nitrophenol (p-NP) and Glu. While p-NP statically quenches an increase in AP-CuCC fluorescence signal, Glu facilitates the production of H2O2 by glucose oxidase during AP-CuCC POD enzyme reactions, triggering colorimetric changes in the reaction. The detection limits for colorimetric and fluorescence measurements were determined to be 0.03 U/L and 0.02 U/L, respectively. By integrating fluorescence analysis, this method cleverly mitigates the confusing effects of normal blood Glu levels on colorimetric outcomes, allowing for the consideration of abnormal Glu levels as a supplementary diagnostic tool. Compared to relying solely on colorimetry, this dual-mode approach reduces false positive rates by 50% and false negative rates by 25%. Leveraging the sensor's colorimetric and fluorescent capabilities provides a versatile platform for precise and reliable evaluation of aberrant expression markers across various clinical settings.

Advancing foodborne pathogen detection: a review of traditional and innovative optical and electrochemical biosensing approaches

Foodborne diseases are a significant cause of morbidity (600 million cases) and mortality (420,000 deaths) worldwide every year and are mainly associated with pathogens. Besides the direct effects on human health, they have relevant concerns related to financial, logistics, and infrastructure for the food and medical industries. The standard pathogen identification techniques usually require a sample enrichment step, plating, isolation, and biochemical tests. This process involves specific facilities, a long-time analysis procedures, and skilled personnel. Conversely, biosensors are an emerging innovative approach to detecting pathogens in real time due to their portability, specificity, sensitivity, and low fabrication costs. These advantages can be achieved from the synergistic work between nanotechnology, materials science, and biotechnology for coupling biomolecules in nano-matrices to enhance biosensing performance. This review highlights recent advancements in electrochemical and optical biosensing techniques for detecting bacteria and viruses. Key properties, such as detection limits, are examined, as they depend on factors like the design of the biorecognition molecule, the type of transducer, the target's characteristics, and matrix interferences. Sensitivity levels reported range from 1 to 1 × 10⁸ CFU/mL, with detection times spanning 10 min to 8 h. Additionally, the review explores innovative approaches, including biosensors capable of distinguishing between live and dead bacteria, multimodal sensing, and the simultaneous detection of multiple foodborne pathogens - emerging trends in biosensor development.

Cascade enzyme-mimicking with spatially separated gold-ceria for dual-mode detection of superoxide anions

Metal-semiconductor nanozyme of dumbbell Au-CeO2 with spatially separated heterostructure has cascade superoxide dismutase (SOD)-like and peroxidase (POD)-like activities for superoxide anions detection. It was synthesized by selective growth of CeO2 at the ends of Au nanorod (Au NR). Taking advantage of the excellent local surface plasmon resonance (LSPR) effect of Au NR, the spatially separated Au-CeO2 has a higher photothermal effect than the continuously growing core-shell structure of Au@CeO2. Meanwhile, the hot electrons of Au NR could transfer to CeO2 under 808 nm laser irradiation, changing the ratio of Ce3+/Ce4+ redox couples over CeO2 and facilitating H2O2 decomposition thus enhancing POD-like activity. Based on the SOD-like activity of Au-CeO2, superoxide anion (O2·-) can be transformed into hydrogen peroxide (H2O2). Dual-mode including absorbance and temperature sensing detection of O2·-, with the detection range from nM to μM i.e., 0.1-150 μM and LOD of 0.033 μM (S/N = 3) was achieved through the cascade catalysis and photothermal effect. The as-proposed method was applicable to both cancer and normal cell samples with satisfactory accuracy and recovery.

Intelligent Screening of Prostate Cancer Individuals Using an Enzyme-Assisted Multicolor Visualization Platform

Rapid and intelligent identification of prostate cancer (PCa) is critical for early diagnosis. Herein, a convenient, reliable, and intelligent strategy is proposed to screen PCa individuals through indirectly quantifying sarcosine (Sar), an early indicator of PCa, in clinical urine samples. Success is achieved by integrating sarcosine oxidase (SOX) as a specific recognition unit; nanozyme-assisted multicolor intelligent visualization platform as a signal reporter. With the Fe-MOFs and peroxidase, the synergetic action of SOX and response gold nanorods (Au NRs) is controlled etched to exhibit a multicolored signal. The sensor exhibits excellent linearity with Sar within 1-60 × 10-6 m, boasting a remarkable detection limit of 0.12 × 10-6 m. The RGB value of the display color can be directly extracted using a mobile phone camera. PCa diagnosis can be swiftly made (within 15 min) and directly by identifying two RGB colors (R < 175 or B > 135). The enzyme-assisted multicolor intelligent visualization platform is adept at detecting minute differences in Sar concentration in urine samples between PCa patients and healthy individuals. The concept of enzyme-assisted multicolor sensing can be further expanded by modifying the type of immobilized enzymes, providing a valuable guideline for the rational design of multiple probes to measure specific biomarkers in biological samples.

Bimetallic FeCo-MOFs mediated Au nanorods etching for the multi-colorimetric and photothermal immunosensing of illegal additive

With the rapid expansion of the health food industry, the scope of safety supervision has also increased. However, traditional instrument detection methods cannot meet the requirements for the rapid on-site detection. Hence, the development of a rapid, precise, and simple method for the analysis of illegal additives in health foods is of great importance. In this work, by using FeCo-MOFs as mimetic peroxidase to mediate Au nanorods (Au NRs) etching, a dual-mode immunosensor based on multi-colorimetric and photothermal signals was fabricated to detect furosemide (FUR). In multi-colorimetric channel, the localized surface plasmon resonance (LSPR) peaks of Au NRs shifted blue, resulting in multi-color changes from red to gray to blue and finally to purple. In photothermal channel, the photothermal effect of Au NRs decreased, resulting in temperature changes. In the range of 1.0 × 10-5-1.0 × 10-2 μg/mL, both LSPR peak blue shift and temperature changes were linearly correlated with the logarithm of FUR concentration, with the detection limits were 4.9 × 10-6 and 8.5 × 10-6 μg/mL, respectively. Furthermore, its concentration can be accurately and intuitively assessed through the observation of vivid colorimetric changes. This advancement offers a highly promising approach for the on-site detection of FUR, facilitating timely and efficient monitoring, thereby significantly enhancing regulatory compliance and ensuring consumer safety.

Etched-suppressed gold nanorods providing highly distinctive plasmonic patterns: Towards multiplex analysis of neuroblastoma biomarkers

BACKGROUND

On-site monitoring of vanillylmandelic acid (VMA), homovanillic acid (HVA), and dopamine (DA) as key diagnostic biomarkers for a wide range of neurological disorders holds utmost significance in clinical settings. Numerous colorimetric sensors with mechanistic approaches based on aggregation or silver metallization have been introduced for this purpose. However, these mechanisms have drawbacks, such as sensitivity to environmental factors and probe toxicity. Therefore, there is a great demand for a robust yet non-toxic colorimetric sensor that employs a novel route to monitor these biomarkers effectively.

RESULTS

Here, we present a single-component multi-colorimetric probe based on the controllable etching suppression of gold nanorods (AuNRs) upon exposure to the mild etchant N-bromosuccinimide (NBS), designed to accurately detect and discriminate VMA, HVA, DA, and their corresponding mixtures, i.e.

, VMA

HVA, VMA:DA, HVA:DA, and VMA:HVA:DA. To enhance the sensitivity and automation capabilities of the designed multi-colorimetric sensor, two machine learning techniques were employed: linear discriminant analysis (LDA) for the qualitative classification and partial least-squares regression (PLSR) for the quantitative analysis of pure biomarkers and their mixtures. The outcomes revealed a high correlation between measured and predicted values, covering a linear range of 0.8-25, 1.2-25, and 2.7-100 μmol L-1, with remarkably low detection limits of 0.260, 0.397, and 0.913 μmol L-1 for VMA, HVA, and DA, respectively. Lastly, the performance of the probe was validated by successfully detecting the neuroblastoma biomarker VMA:HVA in human urine.

SIGNIFICANCE

Our designed multi-colorimetric probe introduces a rapid, cost-effective, user-friendly, non-toxic, and non-invasive approach to detecting and discriminating not only the pure biomarkers but also their corresponding binary and ternary mixtures. The distinctive response profiles produced by the probe in the presence of different mixture ratios can indicate various disease states in patients, which is highly crucial in clinical diagnostics.

Multiprobe Amplification (MPA) with Melting Curve Analysis: A Highly Stable and Cost-Effective Platform for the Simultaneous Detection of Eight Potential Bacterial Bioterrorism Agents in Complex Samples

We aimed to develop an efficient detection platform that can identify a larger number of suspicious samples in a single test, saving time, manpower, and material costs, and providing vital support to the public health system in coping with the current challenging and dynamic bioterrorism threat landscape, particularly in regions of turmoil and conflict. We have successfully developed a high-throughput, multitarget fluorescent array detection platform by effectively combining integrating multiprobe amplification (MPA) with melting curve analysis. Specifically, we have established reliable laboratory testing methods for eight highly pathogenic bacteria, including Bacillus anthracis, Yersinia pestis, Brucella spp., Burkholderia pseudomallei, Francisella tularensis, Vibrio cholerae, Salmonella typhi, and Staphylococcus aureus. Our method achieves sensitive and specific simultaneous detection of eight target bacteria in one well by optimizing the reaction conditions of MPA. In the assessment of 192 simulated environmental samples, both positive and negative coincidence rates were 100.00%. Among 48 simulated clinical samples, the positive coincidence rate reached 97.73%, while maintaining a perfect negative coincidence rate of 100.00%. Moreover, the detection platform holds immense potential for attaining a more comprehensive bioterrorism screening, and its high cost-effectiveness enables the provision of diverse and adaptable diagnostic methods for public health quarantine in underdeveloped countries and regions.

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on a "three-in-one" nanohybrid with high oxidase-like activity for AIEgen

A colorimetry/fluorescence dual-mode assay based on the aptamer-functionalized magnetic covalent organic framework-supported CuO and Au NPs (MCOF-CuO/Au@apt) was developed for Salmonella typhimurium (S. typhimurium) biosensing. The nanohybrid combined three functions in one: good magnetic separation characteristic, excellent oxidase-mimic activity for tetrap-aminophenylethylene (TPE-4A), and target recognition capability. The attachment of MCOF-CuO/Au@apt onto the surface of S. typhimurium resulted in a significant reduction in the oxidase-mimicking activity of the nanohybrid, which could generate dual-signal of colorimetry and fluorescence through the catalytic oxidation of TPE-4A. Based on this, S. typhimurium could be specifically detected in the linear ranges of 102- 106 CFU·mL-1 and 101- 106 CFU·mL-1, with LODs of 7.6 and 2.1 CFU·mL-1, respectively in colorimetry/fluorescence modes. Moreover, the smartphone and linear discrimination analysis-based system could be used for on-site and portable testing. In addition, this platform showed applicability in detecting S. typhimurium in milk, egg liquid and chicken samples.

Photoelectrochemical/Colorimetric Dual-Mode Specific Detection of Staphylococcus aureus Based on the Enzymatic Reaction Triggered by Catalase from Lysed Bacteria

Staphylococcus aureus (S. aureus) is abundant in nature and frequently leads to various health issues. Bacteriophages as obligate intracellular parasites of bacteria have the ability to specifically identify and infect S. aureus, causing bacterial lysis and the release of endogenous catalase (CAT). The released CAT triggers the conversion of H2O2 into O2 and H2O, resulting in a notable decrease in UV absorption at 570 nm and a concurrent surge in photocurrent. On the basis of this, a photoelectrochemical/colorimetric dual-mode biosensor for the detection of S. aureus was developed. In the photoelectric detection mode, the reactions involving endogenous enzymes occur directly in the solution, requiring only the simple drop-coating of TiO2@CdS onto the indium tin oxide (ITO) electrode surface. There was no need for immobilizing additional biomolecules, thereby significantly minimizing nonspecific adsorption and improving the biosensor's stability and reproducibility. For colorimetry, we utilized a cost-effective and operationally simple approach based on KI and starch. Remarkably, this photoelectrochemical/colorimetry exhibited a linear range of 102-109 CFU/mL for S. aureus, achieving detection limits of 7 and 10 CFU/mL, respectively. Herein, phage identification ensures the specific detection of live S. aureus, thereby effectively mitigating the potential for false signals. The dual-signal readout mode improves the detection accuracy and reliability. In conclusion, this present method offers numerous advantages, including simplicity, time-efficiency, cost-effectiveness, high specificity, and therefore excellent accuracy.

Machine learning-enabled colorimetric sensors for foodborne pathogen detection

In the past decade, there have been various advancements to colorimetric sensors to improve their potential applications in food and agriculture. One application of growing interest is sensing foodborne pathogens. There are unique considerations for sensing in the food industry, including food sample destruction, specificity amidst a complex food matrix, and high sensitivity requirements. Incorporating novel technology, such as nanotechnology, microfluidics, and smartphone app development, into colorimetric sensing methodology can enhance sensor performance. Nonetheless, there remain challenges to integrating sensors with existing food safety infrastructure. Recently, increasingly advanced machine learning techniques have been employed to facilitate nondestructive, multiplex detection for feasible assimilation of sensors into the food industry. With its ability to analyze and make predictions from highly complex data, machine learning holds potential for advanced yet practical colorimetric sensing of foodborne pathogens. This article summarizes recent developments and hurdles of machine learning-enabled colorimetric foodborne pathogen sensing. These advancements underscore the potential of interdisciplinary, cutting-edge technology in providing safer and more efficient food systems.

Cascade reaction triggered colorimetric array for identification of organophosphorus pesticides congeners

A modern agriculture uses alternative pest control methods to boost productivity, leading to an accumulation of organophosphorus (OPPs) congeners. This necessitates an intuitive and quick way to identify OPPs congeners. A colorimetric sensor for detecting OPPs congeners using a double-enzyme cascade reaction has been successfully designed and constructed in this study. The OPPs regulate the color changes induced by manganese dioxide nanoflowers (MnO2 NFs) and specific alkaline phosphatases (ALP) during the etching of gold nanopyramids (Au NBPs). The ascorbic acid (AA) produced by ALP hydrolysis inhibits Au NBPs etching by MnO2 NFs oxidized 3, 3', 5, 5'-tetramethylbenzidine (TMB). By inhibiting ALP catalytic activity, OPPs prevent AA formation. In this process, Au NBPs will undergo further etching, resulting in various colors so they can be analyzed semi-quantitatively with the naked eye. It has been found that different types of OPPs inhibit enzymes differently and therefore result in varying degrees of etching of Au NBPs. Principal Component Analysis (PCA) is performed by smart devices that convert R, G, and B signals into digital signals. This colorimetric array tests various foods (tea, apple, and cabbage). Colorimetric visualization sensors combined with data analysis will be used in real-life product development.

High-Resolution and Dynamic Visualization of Intracellular Redox Potential Using a Metal-Organic Framework-Functionalized Nanopotentiometer

Redox potential plays a key role in regulating intracellular signaling pathways, with its quantitative analysis in individual cells benefiting our understanding of the underlying mechanism in the pathophysiological events. Here, a metal organic framework (MOF)-functionalized SERS nanopotentiometer has been developed for the dynamic monitoring of intracellular redox potential. The approach is based on the encapsulation of zirconium-based MOF (Uio-66-F4) on a surface of gold-silver nanorods (Au-Ag NRs) that is modified with the newly synthesized redox-sensitive probe ortho-mercaptohydroquinone (HQ). Thanks to size exclusion of MOF as the chemical protector, the nanopotentiometer can be adapted to long-term use and possess high anti-interference ability toward nonredox species. Combining the superior fingerprint identification of SERS with the electrochemical activity of the quinone/hydroquinone, the nanopotentiometer shows a reversible redox responsivity and can quantify redox potential with a relatively wide range of -250-100 mV. Furthermore, the nanopotentiometer allows for dynamic visualization of intracellular redox potential changes induced by drugs' stimulation in a high-resolution manner. The developed approach would be promising for offering new insights into the correlation between redox potential and tumor proliferation-involved processes such as oxidative stress and hypoxia.

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.

Distinguishable Colorimetric Biosensor for Diagnosis of Prostate Cancer Bone Metastases

Castration-resistant prostate cancer (PCa) causes severe bone metastasis (BM), which significantly increases mortality in men with PCa. Imaging tests and radiometric scanning require long analysis times, expensive equipment, specialized personnel, and a slow turnaround. New visualization technologies are expected to solve the above problems. Nonetheless, existing visualization techniques barely meet the urgency for precise diagnosis because the human eyes cannot recognize and capture even slight variations in visual information. By using dye differentiated superposition enhancement colorimetric biosensors, an effective method to diagnose prostate cancer bone metastases (PCa-BM) with excellent accuracy for naked-eye quantitative detection of alkaline phosphatase (ALP) is developed. The biomarker ALP specific hydrolytic product ascorbic acid can be detected by rhodamine derivatives (Rd) as gold nanobipyramids (Au NBPs) are deposited and grown. Color-recombining enhancement effects between Rd and Au NBPs significantly improved abundance. The 150 U L-1 threshold between normal and abnormal can be identified by color. And with color enhancement effect and double signal response, the ALP index is visually measured to diagnose PCa-BM and provide handy treatment recommendations. Additionally, the proposed colorimetric sensing strategy can be used to diagnose other diseases.

Highly-oxidizing Au@MnO2-X nanozymes mediated homogeneous electrochemical detection of organophosphorus independent of dissolved oxygen

Traditional oxidase-like (OXD) nanozymes rely primarily on O2-mediated superoxide anion (O2·-) process for catalytic oxidation and organophosphorus (Ops) detection. While during the actual detection process, the concentration of O2 is inconstant that can be easily changed with the external environment, distorting detection results. Herein, highly-oxidizing Au@MnO2-X nanozymes with core-shell nanostructure are designed which trigger substantial electron transfer from inner Au core to outer ultrathin MnO2-X layer. According to experimental and theoretical calculations, the core-shell nanostructure and ultrathin MnO2-X of Au@MnO2-X result in the large surface defects, high oxygen vacancies and MnIII ratios. The specially structured Au@MnO2-X nanozymes are therefore highly-oxidizing and the catalytic oxidation can be completed merely through electrons transferring instead of the O2-mediated O2·- process. Based on this, an oxygen independent and ultrasensitive nanozyme-based sensor is established using homogeneous electrochemistry (HEC), its Ops is detected at a LOD of 0.039 ng mL-1. Combined with the UV-vis spectrum of 3,3',5,5'-tetramethylbenzidine (TMB), the linear discriminant analysis of five Ops i.e., Ethion, Omethoate, Diazinon, Chlorpyrifos methyl and Dipterex has achieved superior discrimination results. Therefore, HEC based on strong oxidizing nanozymes provide a new avenue for the development of high-performance electrochemical sensors and demonstrate potential applicability to pesticide residue determination in real samples.

Logic gate-driven dual-index balanced visualization strategy for tumor metastasis diagnosis

Exfoliated tumor cells are integral to malignant tumors diagnosis. The process of clinical cytology of exfoliation involves several complex steps that require at least two days of preparation. Here, we develop a balanced-etching visual kit based on concentration differences of Glutathione/Glucose (GSH/Glu) to distinguish normal from exfoliated tumor cells rapidly and accurately. The balanced-etching visualization kit can be used to obtain color cards and screen exfoliated tumor cells initially (within 10 min). Furthermore, by utilizing logic gates and machine learning algorithms for RGB extraction of the color card obtained from the kit, accurate screening of exfoliated tumor cells is achieved. Finally, a series of clinical tumor samples, such as urine, pleural fluids, ascites, and gastric fluids, have been validated. With effective experimental methods, accurate disease information, and appropriate therapeutic programs, the novel diagnostic strategy is expected to promote precision medicine.

Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays

The drive to achieve ultrasensitive target detection with exceptional efficiency and accuracy requires the advancement of immunoassays. Optical immunoassays have demonstrated significant potential in clinical diagnosis, food safety, environmental protection, and other fields. Through the innovative and feasible combination of enzyme catalysis and optical immunoassays, notable progress has been made in enhancing analytical performances. Among the kinds of reporter enzymes, alkaline phosphatase (ALP) stands out due to its high catalytic activity, elevated turnover number, and broad substrate specificity, rendering it an excellent candidate for the development of various immunoassays. This review provides a systematic evaluation of the advancements in optical immunoassays by employing ALP as the signal label, encompassing fluorescence, colorimetry, chemiluminescence, and surface-enhanced Raman scattering. Particular emphasis is placed on the fundamental signal amplification strategies employed in ALP-linked immunoassays. Furthermore, this work briefly discusses the proposed solutions and challenges that need to be addressed to further enhance the performances of ALP-linked immunoassays.