Search

The development of fluorometric paper-based analytical devices (fPADs) integrated with smartphone for fluorometric quantification of ethanol in an instrument-free and portable setup is described. The NAD + -dependent alcohol dehydrogenase immobilized within chitosan modified paper substate was utilized as a bio-recognition element and enzymatically generated NADH was used as a fluorescent probe. 3D-printed imaging setup which houses a paper chip holder and UV-light emitting device (LED) was developed for rapid, accurate capture of the fluorescent images. The biocompatible chitosan layer covering the paper provides a feasible environment for enzyme immobilization and enhances the fluorescence signal. The developed fPADs exhibited high sensitivity for ethanol detection and has a linear range for ethanol detection from 17 µM to 8.75 mM (R 2 =0.99). Additionally, the fPADs were applied to quantify ethanol in four different wine samples including red, white, rose, and sparkling wines successfully. Moreover, the fPADs produce reproducible signals without loss of enzyme activity for at least 14 days and ~80% activity remained till 28 days. Thus, the proposed approach can provide a facile, affordable, portable, and instrument-free tool for the onsite quantification of ethanol in real samples and is applicable for food quality controls., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Detecting sputum pyocyanin (PYO) with a competitive immunoassay is a promising approach for diagnosing Pseudomonas aeruginosa respiratory infections. However, it is not possible to perform a negative control to evaluate matrix-effects in competitive immunoassays, and the highly complex sputum matrix often interferes with target detection. Here, we show that these issues are alleviated by performing competitive immunoassays with a paper biosensor. The biosensing platform consists of a paper reservoir, which contains antibody-coated gold nanoparticles, and a substrate containing a competing recognition element, which is a piece of paper modified with an albumin-antigen conjugate. Detection of PYO with a limit of detection of 4.7·10 -3  µM and a dynamic range between 4.7·10 -1  µM and 47.6 µM is accomplished by adding the sample to the substrate with the competing element and pressing the reservoir against it for 5 min. When tested with patient samples, the biosensor was able to qualitatively differentiate spiked from non-spiked samples, whereas ELISA did not show a clear cut-off between them. Furthermore, the relative standard deviation was lower when determining sputum with the paper-based biosensor. These features, along with a mild liquefaction step that circumvents the use of harsh chemicals or instruments, make our biosensor a good candidate for diagnosing Pseudomonas infections at the bedside through the detection of sputum PYO., (© 2023. The Author(s).)

Paper-based electrochemical analytical devices (ePADs) have gained significant interest as promising analytical units in recent years because they can be fabricated in simple ways, are low-cost, portable, and disposable platforms that can be applied in various fields. In this sense, paper-based electrochemical biosensors are attractive analytical devices since they can promote diagnose several diseases and potentially allow decentralized analysis. Electrochemical biosensors are versatile, as the measured signal can be improved by using mainly molecular technologies and nanomaterials to attach biomolecules, resulting in an increase in their sensitivity and selectivity. Additionally, they can be implemented in microfluidic devices that drive and control the flow without external pumping and store reagents, and improve the mass transport of analytes, increasing sensor sensitivity. In this review, we focus on the recent developments in electrochemical paper-based devices for viruses' detection, including COVID-19, Dengue, Zika, Hepatitis, Ebola, AIDS, and Influenza, among others, which have caused impacts on people's health, especially in places with scarce resources. Also, we discuss the advantages and disadvantages of the main electrode's fabrication methods, device designs, and biomolecule immobilization strategies. Finally, the perspectives and challenges that need to be overcome to further advance paper-based electrochemical biosensors' applications are critically presented., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Rapid and sensitive detection of enteropathogenic Escherichia coli (EPEC) in fluids with complex background is an important task for safety quality control in the field of medicine, environment, and food. In this study, a gold foil paper-based aptasensor was developed for the detection of enteropathogenic EPEC O26:K60 with surface-enhanced Raman spectroscopy (SERS) and magnetic separation technology mediated by Fe 3 O 4 @Au composite. The gold foil paper was firstly modified with thiolated capture probe and SERS tag. The thiolated aptamer probe for EPEC was immobilized onto a Fe 3 O 4 @Au composite. In the presence of EPEC, highly specific recognition between the aptamer probe and EPEC made the Fe 3 O 4 @Au composite partially dissociated from the gold foil paper. This led to a decreased Raman intensity response, which showed an obvious negative linear correlation with increasing concentration of EPEC over a wide concentration range from 10 to 10 7  CFU/mL under an excitation wavelength of 633 nm. The detection limit was about 2.86 CFU/mL in a buffer solution and a licorice extractum and the detection time was only 2.5 h. The results demonstrate that the gold foil paper-based aptasensor can be an excellent biosensing platform that offers a reliable, rapid, and sensitive alternative for EPEC detection., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

An electroanalytical platform capable to take and dilute the sample has been designed in order to fully integrate the different steps of the analytical process in only one device. The concept is based on the addition of glass-fiber pads for sampling and diluting to an electrochemical cell combining a paper-based working electrode with low-cost connector headers as counter and reference electrodes. In order to demonstrate the feasibility of this all-in-one platform for biosensing applications, an enzymatic sensor for glucose determination (requiring a potential as low as -0.1 V vs. gold-plated wire by using ferrocyanide as mediator) was developed. Real food samples, such as cola beverages and orange juice, have been analyzed with the bioelectroanalytical lab-on-paper platform. As a proof-of-concept, and trying to go further in the integration of steps, sucrose was successfully detected by depositing invertase in the sampling strip. This enzyme hydrolyzes sucrose into fructose and glucose, which was determined using the enzymatic biosensor. This approach opens the pathway for the development of devices applying the lab-on-paper concept, saving costs and time, and making possible to perform decentralized analysis with high accuracy., (© 2021. The Author(s).)

Enzyme-linked immunosorbent assay (ELISA) is widely used for the detection of disease biomarkers. However, it utilizes time-consuming procedures and expensive instruments, making it infeasible for point-of-care (POC) analysis especially in resource-limited settings. In this work, a multicolorimetric ELISA biosensor integrated on a paper/polymer hybrid microfluidic device was developed for rapid visual detection of disease biomarkers at point of care, without using costly equipment. This multicolormetric ELISA platform was built on multiple distinct color variants resulted from the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and the etching of gold nanorods (AuNRs). The vivid color changes could be easily distinguished by the naked eye, and their red mean values allowed quantitative biomarker detection, without using any sophisticated instruments. When this multicolorimetric ELISA was integrated on a paper/polymer hybrid analytical device, it not only provided integrated processing and high portability but also enabled fast assays in about 50 min due to the unique advantages of paper/polymer hybrid devices. The limit of detection of 9.1 ng/μL of the hepatitis C virus core antigen, a biomarker for hepatitis C, was achieved using this multicolorimetric ELISA platform. This multicolor ELISA analytical device provides a new versatile, user-friendly, affordable, and portable immunosensing platform with high potential for on-site detections of various viruses, proteins, and biomarkers for low-resource settings such as at home, public venues, rural areas, and developing nations.

Bacillus cereus is one of the most common foodborne pathogens found in various kinds of staple foods such as rice and wheat. A rapid and accurate detection method for this pathogen is highly desirable for the sustainable production of relevant food products. While several classical and molecular-based detection methods are available for the identification of B. cereus, they suffered one or more limitations such as the requirement for a tedious and time-consuming process, less than ideal specificity, and the lack of portability. Herein, we developed the first paper-based sensing device that exhibits high species specificity with sufficiently low limit of detection for the visual detection of specific DNA sequences of B. cereus. The success is attributed to the strategic planning of fabrication in various dimensions including thorough bioinformatics search for highly specific genes, the use of the pyrrolidinyl peptide nucleic acid (PNA) probe whose selectivity advantage is well documented, and an effective PNA immobilization and DNA-binding visualization method with an internal cross-checking system for validating the results. Testing in rice matrices indicates that the sensor is capable of detecting and distinguishing B. cereus from other bacterial species. Hence, this paper-based sensor has potential to be adopted as a practical means to detect B. cereus in food industries., (© 2021. Springer-Verlag GmbH Germany, part of Springer Nature.)

Paper has been widely employed as cheap material for the development of a great number of sensors such as pregnancy tests, strips to measure blood sugar, and COVID-19 rapid tests. The need for new low-cost analytical devices is growing, and consequently the use of these platforms will be extended to different assays, both for the final consumer and within laboratories. This work describes a paper-based electrochemical sensing platform that uses a paper disc conveniently modified with recognition molecules and a screen-printed carbon electrode (SPCE) to achieve the detection of gluten in a deep eutectic solvent (DES). This is the first method coupling a paper biosensor based on aptamers and antibodies with the DES ethaline. Ethaline proved to be an excellent extraction medium allowing the determination of very low gluten concentrations. The biosensor is appropriate for the determination of gluten with a limit of detection (LOD) of 0.2 mg L -1 of sample; it can detect gluten extracted in DES with a dynamic range between 0.2 and 20 mg L -1 and an intra-assay coefficient of 10.69%. This approach can be of great interest for highly gluten-sensitive people, who suffer from ingestion of gluten quantities well below the legal limit, which is 20 parts per million in foods labeled gluten-free and for which highly sensitive devices are essential., (© 2021. The Author(s).)

A paper-based electrochemical dual-function biosensor capable of determining pH and TCO 2 was synthesized for the first time using an iridium oxide pH electrode and an all-solid-state ion electrode (ASIE). In the study, to obtain highly reliable results, the biosensor was equipped with a real-time pH correction function before TCO 2 measurements. Compared to traditional liquid-filling carbon dioxide detection sensors, the utilization of ferrocene endows our novel sensor with abundant positive sites, and thus greatly improves its performance. Conversely, the introduction of MXene with conductivity close to that of metals reduces electrode resistance, which is beneficial for accelerating the electrochemical reaction of the sensor and reducing LOD. After optimization, the detection range of TCO 2 is 0.095 nM-0.66 M, with a detection limit of as low as 0.023 nM. In addition, the sensor was used in real serum sample-spiked recovery experiments and comparison experiments with existing clinical blood gas analyzers, which confirmed the effectiveness of its clinical application. This study provides a method for the rational design of paper-based electrochemical biosensors and a new approach for the clinical detection of blood carbon dioxide., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Centralized laboratories in which analytical processes are automated to enable the analysis of large numbers of samples at relatively low cost are used for analytical testing throughout the world. However, healthcare is changing, partly due to the general recognition that care needs to be more patient-centered and putting the patient at the center of action. One way to achieve this goal is to consider point-of-care testing (PoC) devices as alternative analytical concepts. This requires miniaturization of current analytical concepts and the use of cost-effective diagnostic tools with appropriate sensitivity and specificity. Electrochemical sensors are ideally adapted as they provide robust, low-cost, and miniaturized solutions for the detection of variable analytes, yet lack the high sensitivity comparable to more classical diagnosis approaches. Advances in nanotechnology have opened up a plethora of different nanomaterials to be applied as electrode and/or sensing materials in electrochemical biosensors. The choice of materials significantly influences the sensor's sensitivity, selectivity, and overall performance. A critical review of the state of the art with respect to the development of the utilized materials (between 2019 and 2023) and where the field is heading to are the focus of this article., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Strontium-90 ( 90 Sr) is a major radioactive component that has attracted great attention, but its detection remains challenging since there are no specific energy rays indicative of its presence. Herein, a biosensor that is capable of rapidly detecting Sr 2+ ions is demonstrated. Simple colorimetric method for sensitive detection of Sr 2+ with the help of single-stranded DNA was developed by preparing MnO 2 nanorods as oxidase mimic catalysis 3,3',5,5'-tetramethylbenzidine (TMB). Under weakly acidic conditions, MnO 2 exhibited a strong oxidase-mimicking activity to oxidize colorless TMB into blue oxidation products (oxTMB) with discernible absorbance signals. Nevertheless, the introduction of a guanine-rich DNA aptamer inhibited MnO 2 -mediated TMB oxidation and reduced oxTMB formation, resulting in blue fading and diminished absorbance. Upon the addition of strontium ions to the system, the aptamers formed a stable G-quadruplex structure with strontium ions, thereby restoring the oxidase-mimicking activity of MnO 2 . Under the best experimental conditions, the absorbance exhibits a linear relationship with the Sr 2+ concentration within the range 0.01-200 μM, with a limit of detection of 0.0028 µM. When the concentration of Sr 2+ from 10 -8 to 10 -6  mol L -1 , a distinct color change gradient could be observed in paper-based sensor. We successfully applied this approach to determine Sr 2+ in natural water samples, obtaining recoveries ranging from 97.6 to 103% with a relative standard deviation of less than 5%. By providing technical solutions for detection, our work contributed to the effective monitoring of transportation of radioactive Sr in the environment., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Bisphenol A (BPA), an important endocrine disrupting compound, has infiltrated human daily lives through electronic devices, food containers, and children's toys. Developing of novel BPA assay methods with high sensitivity holds tremendous importance in valuing the pollution state. Here, we constructed an ultrasensitive photoelectrochemical (PEC) aptasensor for BPA determination by regulating photoactivities of CdS/Ni-based metal-organic framework (CdS/Ni-MOF) with [Ru(bpy) 2 dppz] 2+ sensitizer. CdS/Ni-MOF spheres exhibited excellent photocatalytic performance, serving as a potential sensing platform for the construction of target recognition process. [Ru(bpy) 2 dppz] 2+ were embedded into DNA double-stranded structure, functioning as sensitizer for modulating the signal response of the developed PEC aptasensor. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (0.1 to 1000.0 nM), low detection limit (0.026 nM, at 3σ/m), excellent selectivity, and high stability. This work provides a perspective for the design of ideal photosensitive materials and signal amplification strategies and extends their application in environment analysis., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A natural stress response induces elevated cortisol levels in biological fluids, such as saliva. While current sensor technologies can detect cortisol in real time, their sensitivity and reliability for human subjects have not been assured. This is due to relatively low concentrations of salivary cortisol, which fluctuate throughout the day and vary significantly between individuals. To address these challenges, we present an improved electrochemical biosensor leveraging graphene's exceptional conductivity and physicochemical properties. A 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE-NHS)-modified commercial graphene foam (GF) electrode is presented to realize an ultra-sensitive biosensor for cortisol detection directly in human saliva. The biosensor fabrication process entails the attachment of anti-cortisol monoclonal antibodies (mAb-cort) onto a PBASE-NHS/GF electrode through noncovalent immobilization on the vertically stratified graphene foam electrode surface. This unique immobilization strategy preserves graphene's structural integrity and electrical conductivity while facilitating antibody immobilization. The binding of cortisol to immobilized mAb-cort is read out via differential pulse voltammetry using ferri/ferro redox reactions. The immunosensor demonstrates an exceptional dynamic range of 1.0 fg mL -1 to 10,000 pg mL -1 (R 2  = 0.9914) with a detection limit of 0.24 fg mL -1 (n = 3) for cortisol. Furthermore, we have established the reliability of cortisol sensors in monitoring human saliva. We have also performed multiple modes of validation, one against the established enzyme-linked immunosorbent assay (ELISA) and a second by a third-party service Salimetric on 16 student volunteers exposed to different stress levels, showing excellent correlation (r = 0.9961). These findings suggest the potential for using mAb-cort/PBASE-NHS/GF-based cortisol electrodes for monitoring salivary cortisol in the general population., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A new conductive ink based on the addition of carbon black to a poly(vinyl alcohol) matrix is developed and investigated for electrochemical sensing and biosensing applications. The produced devices were characterized using morphological and electrochemical techniques and modified with Pd nanoparticles to enhance electrical conductivity and reaction kinetics. With the aid of chemometrics, the parameters for metal deposition were investigated and the sensor was applied to the determination of Parkinson's disease biomarkers, specifically epinephrine and α-synuclein. A linear behavior was obtained in the range 0.75 to 100 μmol L -1 of the neurotransmitter, and the device displayed a limit of detection (LOD) of 0.051 μmol L -1 . The three-electrode system was then tested using samples of synthetic cerebrospinal fluid. Afterward, the device was modified with specific antibodies to quantify α-synuclein using electrochemical impedance spectroscopy. In phosphate buffer, a linear range was obtained for α-synuclein concentrations from 1.5 to 15 μg mL -1 , with a calculated LOD of 0.13 μg mL -1 . The proposed immunosensor was also applied to blood serum samples, and, in this case, the linear range was observed from 6.0 to 100.5 μg mL -1 of α-synuclein, with a LOD = 1.3 µg mL -1 . Both linear curves attend the range for the real diagnosis, demonstrating its potential application to complex matrices., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Amino acid L-arginine (Arg), usually presented in food products and biological liquids, can serve both as a useful indicator of food quality and an important biomarker in medicine. The biosensors based on Arg-selective enzymes are the most promising devices for Arg assay. In this research, three types of amperometric biosensors have been fabricated. They exploit arginine oxidase (ArgO), recombinant arginase I (ARG)/urease, and arginine deiminase (ADI) coupled with the ammonium-chelating redox-active nanoparticles. Cadmium-copper nanoparticles (nCdCu) as the most effective nanochelators were used for the development of ammonium chemosensors and enzyme-coupled Arg biosensors. The fabricated enzyme/nCdCu-containing bioelectrodes show wide linear ranges (up to 200 µM), satisfactory storage stabilities (14 days), and high sensitivities (A⋅M -1 ⋅m -2 ) to Arg: 1650, 1700, and 4500 for ADI-, ArgO- and ARG/urease-based sensors, respectively. All biosensors have been exploited to estimate Arg content in commercial juices. The obtained data correlate well with the values obtained by the reference method. A hypothetic scheme for mechanism of action of ammonium nanochelators in electron transfer reaction on the arginine-sensing electrodes has been proposed., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Self-powered immunosensors (SPIs) based on enzymatic biofuel cell (EBFC) have low sensitivity and poor stability due to the high impedance of the immune sandwich and the vulnerability of enzymes to environmental factors. Here, we applied the Faraday cage-type sensing mode on a hybrid biofuel cell (HBFC)-based SPI for the first time, which exhibited high sensitivity and stability. Cytokeratin 19 fragment (CYFRA 21-1) was used as a model analyte. Au nanoparticle-reduced graphene oxide (Au-rGO) composite was used as the supporting matrix for immunoprobe immobilized with detection antibody and glucose dehydrogenase (GDH), also the builder for Faraday cage structure on the bioanode in the presence of antigen. After the combination of immunoprobe, antigen, and the antibody on the bioanode, the Faraday cage was constructed in case the AuNP-rGO was applied as a conductive cage for electron transfer from GDH to the bioanode without passing through the poorly conductive protein. With the assistance of the Faraday cage structure, the impedance of the bioanode decreased significantly from 4000 to 300 Ω, representing a decline of over 90%. The sensitivity of the SPI, defined as the changes of open circuit voltage (OCV) per unit concentration of the CYFRA 21-1, was 68 mV [log (ng mL -1 )] -1 . In addition, Fe-N-C was used as an inorganic cathode material to replace enzyme for oxygen reduction reaction (ORR), which endowed the sensor with 4-week long-term stability. This work demonstrates a novel sensing platform with high sensitivity and stability, bringing the concept of hybrid biofuel cell-based self-powered sensor., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Biosensors have been widely used for bacteria determination with great success. However, the "lock-and-key" methodology used by biosensors to identify bacteria has a significant limitation: it can only detect one species of bacteria. In recent years, optical (fluorescent and colorimetric) sensor arrays are gradually gaining attention from researchers as a new type of biosensor. They can acquire multiple features of a target simultaneously, form a feature pattern, and determine the bacteria species with the help of pattern recognition/machine learning algorithms. Previous reviews in this area have focused on the interaction between the sensor array and bacteria or the materials used to make the sensors. This review, on the other hand, will provide researchers with a better understanding of the field by discussing fluorescent and colorimetric sensor arrays based on the mechanism of optical signal generation. These sensor arrays will be compared based on the identified species. Finally, we will discuss the limitations of these sensor arrays and explore possible solutions., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

An ochratoxin A (OTA) electrochemical biosensor based on a cascade signal amplification strategy with Ag nanoparticles (AgNPs) and ring opening polymerization (ROP) was constructed. The large specific surface area of AgNPs was used to increase the loading of OTA aptamer on the electrode surface, enhancing the ability to capture OTA as a way to achieve the first signal amplification. The OTA antibody modified with polyethylenimine specifically recognizes the OTA, forming an aptamer-OTA-antibody sandwich structure. The amino group on polyethylenimine initiates the ROP reaction with α-amino acid-n-carboxylic anhydride-ferrocene (NCA-Fc) as the monomer. A large number of electrochemical signal units of ferrocene are introduced into the sensing system for a second signal amplification. By amplifying the signal twice, the sensitivity of the sensor is improved. Under the optimal conditions, the detection range of the sensor is 1 pg·mL -1  ~ 1 μg·mL -1 , while the detection limit is as low as 117 fg·mL -1 . Moreover, the sensor has the advantages of high sensitivity, good stability and selectivity. Standard addition recovery experiment proved that the sensing system can be successfully used for the detection of OTA in four actual samples with recoveries in the range 90.0 to 113% with RSDs of 0.6 to 5.2%, providing a new idea for the pollution assessment of mycotoxins., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Pesticides, chemical substances extensively employed in agriculture to optimize crop yields, pose potential risks to human and environmental health. Consequently, regulatory frameworks are in place to restrict pesticide residue concentrations in water intended for human consumption. These regulations are implemented to safeguard consumer safety and mitigate any adverse effects on the environment and public health. Although gas chromatography- and liquid chromatography-mass spectrometry (GC-MS and LC-MS) are highly efficient techniques for pesticide quantification, their use is not suitable for real-time monitoring due to the need for sophisticated laboratory pretreatment of samples prior to analysis. Since they would enable analyte detection with selectivity and sensitivity without sample pretreatment, biosensors appear as a promising alternative. These consist of a bioreceptor allowing for specific recognition of the target and of a detection platform, which translates the biological interaction into a measurable signal. As early detection systems remain urgently needed to promptly alert and act in case of pollution, we review here the biosensors described in the literature for pesticide detection to advance their development for use in the field., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Detection of oral pathogens is essential in the management of oral diseases, as their occurrence and progression are closely linked to an imbalance in these microorganisms. Detection techniques such as microbial cultures, enzyme-linked immunosorbent assays and polymerase chain reactions are highly dependent on complex testing procedures and specialized laboratory equipment, making prevention and early diagnosis of oral diseases difficult. To comprehensively implement oral disease prevention and early diagnosis in social groups, there is an urgent need for portable testing methods for oral pathogenic bacteria that can be applied in community and home settings. In this review, several common portable biosensors for pathogenic bacteria are first described. Based on the goal of achieving primary prevention and diagnosis of oral diseases, we elaborate and summarize portable biosensors for common oral pathogenic bacteria in terms of how to achieve portability of the technique. This review aims to reflect the current status of portable biosensors for common oral pathogens and to lay the foundation for the further realization of portable detection of oral pathogens., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

Sepsis, an infectious disease affecting millions of people's health worldwide each year, calls for urgent attention to an improvement of analytical devices. Chemiluminescence immunoassay is a typical diagnostic method utilized to assess the risk development of sepsis. However, due to its high-cost, delayed, and complicated procedure, the practical utilization is therefore undoubtedly limited, especially for point-of-care test. Herein, we fabricated for the first time an immunosensor based on dendritic copper nanostructures (CuNSs) combined with 4-aminobenzoic acid (4-AB, the diazonium salt) as antibody linker modified on a screen-printed graphene electrode for the early detection of the sepsis biomarker interleukin-6 (IL-6). The electrode fabrication is made by electrodeposition, thus eliminating the multistep of nanomaterial synthesis and time wasting. The resulting dendritic CuNSs significantly increase the effective surface area (1.2 times) and the sensor's performance. The morphology of this combination was characterized using CV, EIS, SEM, EDX, and FTIR techniques. In the detection process, the appearance of IL-6 suppresses the current response of the redox probe indicator measured by differential pulse voltammetry due to the antibody-antigen complex. The subtraction of signal (ΔI) was interpreted as IL-6 concentration. This sensor exhibited a linear range from 0.05 to 500 pg mL -1 with low detection limit of 0.02 pg mL -1 , proving a possibility for early sepsis screening. In addition, the established immunosensor can successfully quantify IL-6 in human serum sample, in which the results agreed well with those achieved using the standard approach, further showing high practical applicability of this developed immunosensor., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

In this present study, we explored the catalytic behaviors of the in situ generated metal nanoparticles, i.e., Pt/Ni, embedded in laser-induced carbon nanofibers (LCNFs) and their potential for H 2 O 2 detection under physiological conditions. Furthermore, we demonstrate current limitations of laser-generated nanocatalyst embedded within LCNFs as electrochemical detectors and possible strategies to overcome the issues. Cyclic voltammetry revealed the distinctive electrocatalytic behaviors of carbon nanofibers embedding Pt and Ni in various ratios. With chronoamperometry at  +0.5 V, it was found that modulation of Pt and Ni content affected only current related to H 2 O 2 but not other interfering electroactive substances, i.e., ascorbic acid (AA), uric acid (UA), dopamine (DA), and glucose. This implies that the interferences react to the carbon nanofibers regardless of the presence of metal nanocatalysts. Carbon nanofibers loaded only with Pt and without Ni performed best in H 2 O 2 detection in phosphate-buffered solution with a limit of detection (LOD) of 1.4 µM, a limit of quantification (LOQ) of 5.7 µM, a linear range from 5 to 500 µM, and a sensitivity of 15 µA mM -1  cm -2 . By increasing Pt loading, the interfering signals from UA and DA could be minimized. Furthermore, we found that modification of electrodes with nylon improves the recovery of H 2 O 2 spiked in diluted and undiluted human serum. The study is paving the way for the efficient utilization of laser-generated nanocatalyst-embedding carbon nanomaterials for non-enzymatic sensors, which ultimately will lead to inexpensive point-of-need devices with favorable analytical performance., (© 2023. The Author(s).)

MicroRNAs (miRNAs) are clinical biomarkers for various human diseases, including cancer. They have been found in liquid biopsy samples, including various bodily fluids. They often play an important role in the early diagnosis and prognosis of cancer, and the development of simple and effective analytical methods would be of pivotal importance for the entire community. The determination of these targets may be affected by the different physicochemical parameters of the specimen of interest. In this work, an electrochemical detection platform for miRNA based on a screen-printed gold electrode was developed. In the present study, miRNA-21 was selected as a model sequence, due to its role in prostate, breast, colon, pancreatic, and liver cancers. A DNA sequence modified with methylene blue (MB) was covalently bound to the electrochemical strip and used to detect the selected target miRNA-21. After optimization of selected parameters in standard solutions, including the study of the effect of pH, the presence of interferent species, and NaCl salt concentration in the background, the application of square-wave voltammetry (SWV) technique allowed the detection of miRNA-21 down to a limit in the order of 2 nM. The developed device was then applied to several urine samples. In this case too, the device showed high selectivity in the presence of the complex matrix, satisfactory repeatability, and a limit of detection in the order of magnitude of nM, similarly as what observed in standard solutions., (© 2023. The Author(s).)

The detection and/or quantification of biomarkers in blood is important for the early detection, diagnosis, and treatment of a variety of diseases and medical conditions. Among the different types of sensors for detecting molecular biomarkers, such as proteins, nucleic acids, and small-molecule drugs, affinity-based electrochemical sensors offer the advantages of high analytical sensitivity and specificity, fast detection times, simple operation, and portability. However, biomolecular detection in whole blood is challenging due to its highly complex matrix, necessitating sample purification (i.e., centrifugation), which involves the use of bulky, expensive equipment and tedious sample-handling procedures. To address these challenges, various strategies have been employed, such as purifying the blood sample directly on the sensor, employing micro-/nanoparticles to enhance the detection signal, and coating the electrode surface with blocking agents to reduce nonspecific binding, to improve the analytical performance of affinity-based electrochemical sensors without requiring sample pre-processing steps or laboratory equipment. In this article, we present an overview of affinity-based electrochemical sensor technologies that employ these strategies for biomolecular detection in whole blood., (© 2023. The Author(s).)

Pathogenic bacterial infection is one of the principal causes affecting human health and ecosystems. The accurate identification of bacteria in food and water samples is of significant interests to maintain safety and health for humans. Culture-based tests are practically tedious and may produce false-positive results, while viable but non-culturable microorganisms (NCMs) cannot be retrieved. Thus, it requires fast, reliable, and low-cost detection strategies for on-field analysis and point-of-care (POC) monitoring. The standard detection methods such as nucleic acid analysis (RT-PCR) and enzyme-linked immunosorbent assays (ELISA) are still challenging in POC practice due to their time-consuming (several hours to days) and expensive laboratory operations. The optical (surface plasmon resonance (SPR), fluorescence, and surface-enhanced Raman scattering (SERS)) and electrochemical-based detection of microbes (early stage of infective diseases) have been considered as alternative routes in the emerging world of nanostructured biosensing since they can attain a faster and concurrent screening of several pathogens in real samples. Moreover, optical and electrochemical detection strategies are opening a new route for the ability of detecting pathogens through the integration of cellphones, which is well fitted for POC analysis. This review article covers the current state of sensitive mechanistic approaches for the screening and detection of Escherichia coli O157:H7 (E. coli) pathogens in food and water samples, which can be potentially applied in clinical and environmental monitoring., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

Since its discovery in 2007, polydopamine nanofilms have been widely used in many areas for surface functionalization. The simple and low-cost preparation method of the nanofilms with tunable thickness can incorporate amine and oxygen-rich chemical groups in virtually any interface. The remarkable advantages of this route have been successfully used in the field of electrochemical sensors. The self-adhesive properties of polydopamine are used to attach nanomaterials onto the electrode's surface and add chemical groups that can be explored to immobilize recognizing species for the development of biosensors. Thus, the combination of 2D materials, nanoparticles, and other materials with polydopamine has been successfully demonstrated to improve the selectivity and sensitivity of electrochemical sensors. In this review, we highlight some interesting properties of polydopamine and some applications where polydopamine plays an important role in the field of electrochemical sensors., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

A sensitive electrochemical strategy for carcinoembryonic antigen 15-3 (CA15-3) detection is reported using CTAB-Co-MOFs@AuPt NPs as signal probes. The electrochemical strategy was designed as follows: First, the graphene aerogel@gold nanoparticles (GA@Au NPs) nanocomposites were employed to modify the sensing surface for promoting electron transfer rate and primary antibody (Ab 1 ) immobilization due to GA possesses a large specific surface area, eminent conductivity, and a 3D network structure. Cobalt metal-organic frameworks (CTAB-Co-MOFs) synthesized were then used as a carrier for AuPt NPs and secondary antibody (Ab 2 ) immobilization (notes: labelled-Ab 2 ). With sandwich immunoreaction, the labelled-Ab 2 was captured on the surface of the GA@Au NPs nanocomposites. Finally, differential pulse voltammetry (DPV) was employed to register the electrochemical signal of the immunosensor at the potential of - 0.85 V (vs SCE) in phosphate buffer saline (PBS) containing 2.5 mM H 2 O 2 . It was verified that the electrochemical reduction signal from Co 3+ to Co 2+ was recorded. The AuPt NPs could catalyze the reaction of H 2 O 2 oxidizing Co 2+ to Co 3+ , resulting in the amplification of the electrochemical signal. Under the selected conditions, the immunosensor can detect CA15-3 in the range 10 µU/mL to 250 U/mL with a low detection limit of 1.1 µU/mL. In the designed strategy, the CTAB-Co-MOFs were not only employed as carriers for AuPt NPs, but also acted as signal probes. The CTAB-Co-MOFs were investigated including SEM, TEM, XPS, and XRD. The application ability of the immunosensor was evaluated using serum sample, demonstrating the immunosensor can be applied to clinic serum analysis., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

An enzyme immunoassay was developed based on the coulometric measurement of immunoglobulin M (IgM) against Hantaan viruses (HTNV) by using virus-like particles (VLPs) as recognition molecules. The surface functionalization of screen-printed carbon electrodes (SPCEs) was achieved through paste-exfoliated graphene that was modified with a COOH group and a thionine mediator through supramolecular-covalent scaffolds, on SPCEs by using the binder contained in the ink. After the covalent immobilization of the antibody, the sensor was used for the sandwich enzyme immunoassay of IgM against HTNV. By using HTNV VLPs as the second recognization molecules, the resulting sensor efficiently monitored the reaction of IgM against HTNV and anti-IgM antibody with high specificity. By attaching HTNV nucleocapsid protein antibody conjugate with horseradish peroxidase (HRP) onto VLPs, the signal response of the assay was derived from the coulometric measurement of H 2 O 2 reduction mediated by thionine on the electrode surface after the application of a potential (- 0.2 V vs. Ag/AgCl). The ratio of charges measured before or after H 2 O 2 addition was used to quantify IgM because these charges could be used as background charges or total charges, respectively. The ratio exhibited good agreement with IgM concentration within a range 0.1 to 1000 pg mL -1 , and a detection limit of 0.06 pg mL -1 was obtained. The assay demonstrated high sensitivity and specificity toward HTNV-specific IgM in serum., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

After optimizing the original aptamer sequence by truncation strategy, a magnetic separation-assisted DNAzyme-driven 3D DNA walker fluorescent aptasensor was developed for detecting the food-borne pathogen Cronobacter species. Iron oxide magnetic nanoparticles (MNPs) modified with a hybrid of truncated aptamer probe and DNAzyme strand (AP-E1) denoted as MNPs@AP-E1, were employed as capture probes. Simultaneously, a DNAzyme-driven 3D-DNA walker was utilized as the signal amplification element. The substrate strand (Sub) was conjugated with the gold nanoparticles (AuNPs), resulting in the formation of AuNPs@Sub, which served as a 3D walking track. In the presence of the target bacteria and Mg 2+ , E1-DNAzyme was activated and moved along AuNPs@Sub, continuously releasing the signal probe. Under optimized conditions, a strong linear correlation was observed for Cronobacter sakazakii (C. sakazakii) in the concentration range 10 1 to 10 6 CFU mL -1 , with a low detection limit of 2 CFU mL -1 . The fluorescence signal responses for different Cronobacter species exhibited insignificant differences, with a relative standard deviation of 3.6%. Moreover, the aptasensor was successfully applied to determine  C. sakazakii in real samples with recoveries of 92.86%-108.33%. Therefore, the novel method could be a good candidate for ultra-sensitive and selective detection of Cronobacter species without complex manipulation., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Acetamiprid (ACE) is a highly effective broad-spectrum insecticide, and its widespread use is potentially harmful to human health and environmental safety. In this study, magnetic Fe 3 O 4 /carbon (Fe 3 O 4 /C), a derivative of metal-organic framework MIL-101 (Fe), was synthesized by a two-step calcination method. And a fluorescent sensing strategy was developed for the efficient and sensitive detection of ACE using Fe 3 O 4 /C and multiple complementary single-stranded DNA (ssDNA). By using aptamer with multiple complementary ssDNA, the immunity of interference of the aptasensor was improved, and the aptasensor showed high selectivity and sensitivity. When ACE was present, the aptamer (Apt) combined with ACE. The complementary strand of Apt (Cs1) combined with two short complementary strands of Cs1, fluorophore 6-carboxyfluorescein-labeled complementary strand (Cs2-FAM) and the other strand Cs3. The three strands formed a double-stranded structure, and fluorescence would not be quenched by Fe 3 O 4 /C. In the absence of ACE, Cs2-FAM would be in a single-chain state and would be adsorbed by Fe 3 O 4 /C, and the fluorescence of FAM would be quenched by Fe 3 O 4 /C via photoelectron transfer. This aptasensor sensitively detected ACE over a linear concentration range of 10-1000 nM with a limit of detection of 3.41 nM. The recoveries of ACE spiked in cabbage and celery samples ranged from 89.49% to 110.76% with high accuracy., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

The blood levels of cancer antigen 125 (CA125) and human epididymal secretory protein 4 (HE4) are measured in the diagnosis and progression monitoring of ovarian cancer (OC), and the Risk of Ovarian Malignancy Algorithm (ROMA) score% values are calculated for cancer risk assessment. For the first time, disposable dual screen-printed carbon electrodes modified with reduced graphene oxide, polythionine, and gold nanoparticles were used to fabricate label-free electrochemical dual CA125-HE4 immunosensors for the sensitive, fast, and practical simultaneous determination of CA125 and HE4. DPV and SWV methods were used to simultaneously determine antigens in two different linear ranges (1-100 pg mL -1 and 1-50 ng mL -1 ). High sensitivity, low LOD, and LOQ were obtained for two linear ranges with a correlation coefficient above 0.99. The application stability of the dual CA125-HE4 immunosensors was determined as 60 days, and the storage stability was determined as 16 weeks. The dual immunosensors exhibited high selectivity in eight different antigen mixtures. The reusability of the dual immunosensors has been tested up to 9 cycles. ROMA score% values for pre-menopausal and post-menopausal status were calculated using the concentration of CA125 and HE4 in the blood serum and assessing OC risk. The disposable dual immunosensors can be used in point-of-care tests for rapid and practical simultaneous determination of CA125 and HE4 with high selectivity, sensitivity, and repeatability., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

Recent years have shown that the diagnosis and monitoring of biomarkers involved in inflammatory-associated medical conditions such as cancer, neurological disorders, viral infections, or daily physical activities offer real benefits in increasing the quality of medical care and patient life quality. In this context, the use of integrated and portable platforms as point-of-care testing devices for biomedical analysis to enable early disease diagnosis and monitoring, which can be successfully used even at the patient's bed, is an emergency nowadays. The development of low-cost, miniaturized, and portable, user-friendly devices that provide an answer in a timely manner, such as electrochemical sensors, is relevant for the elaboration of point-of-care testing devices. This review focuses on the recent progress in bioanalysis of both specific biomarkers and inflammatory-associated biomarkers present in several diseases like neoplasia, severe neurological disorders, viral infections, and usual physical activity and provides an overview of the state of the art over the most recent electrochemical (bio)sensors for the detection of inflammation-related biomarkers. Future perspectives of point-of-care testing to improve healthcare management are also discussed., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

To tackle cancer and provide prompt diagnoses and prognoses, the constantly evolving biosensing field is continuously on the lookout for novel markers that can be non-invasively analysed. Extracellular vesicles (EVs) may represent a promising biomarker that also works as a source of biomarkers. The augmented cellular activity of cancerous cells leads to the production of higher numbers of EVs, which can give direct information on the disease due to the presence of general and cancer-specific surface-tethered molecules. Moreover, the intravesicular space is enriched with other molecules that can considerably help in the early detection of neoplasia. Even though EV-targeted research has indubitably received broad attention lately, there still is a wide lack of practical and effective quantitative procedures due to difficulties in pre-analytical and analytical phases. This review aims at providing an exhaustive outline of the recent progress in EV detection using electrochemical and photoelectrochemical biosensors, with a focus on handling approaches and trends in the selection of bioreceptors and molecular targets related to EVs that might guide researchers that are approaching such an unstandardised field., (© 2023. The Author(s).)

Nanozymes have been emerging as substitutes for natural enzymes to construct biosensors towards biomolecular detection. However, the detection of glutathione (GSH) by nanozyme-based biosensors still remains a great challenge for research on catalytic activity enhancement and the detection mechanism. In this work, Sb-doped iron oxychloride (Sb-FeOCl) with a well-defined nanorod-like structure is prepared by high-temperature calcination. Sb-FeOCl nanorods have high peroxidase-like activity, which can catalyze the decomposition of H 2 O 2 into ·OH and then oxidize 3,3',5,5'-tetramethylbenzidine (TMB). In view of these intriguing observations, a reliable colorimetric method with a simple mixing and detection strategy is developed for the detection of GSH. The linear range of GSH detection is 1-36 μM. The detection limit of GSH reaches a low level of 0.495 μM (3σ/slope). The GSH sensing system also exhibits excellent specificity and anti-interference. Taking advantage of the advantages of the Sb-FeOCl nanorod-based biosensor, it can be used to quantitatively detect GSH levels in human serum. It can be anticipated that the Sb-FeOCl nanorods have broad prospects in the field of enzymatic biochemical reactions., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

An assembled-aptasensor based on Fe 3 O 4 @Au@Ag nanocomposites grafting onto the gold foil was prepared, which can be developed into a universal approach for sensitive and rapid detection of various pathogenic bacteria, such as Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium), Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes), Pseudomonas aeruginosa (P. aeruginosa), and Shigella flexneri (S. flexneri). Firstly, the gold foil paper was modified with thiolated capture probe and SERS tag in proportion, and at the same time, the specific thiolated aptamer probe for corresponding pathogenic bacteria was fixed with Fe 3 O 4 @Au@Ag nanocomposites. An obvious Raman signal can be subsequently increased about 10 6 times by the external electromagnetic field enhancement at the "hot spots" caused by the hybridization of aptamer and capture probe. But in the presence of target pathogenic bacteria, Raman intensity will decrease as Fe 3 O 4 @Au@Ag nanocomposites are dissociated from gold foil. Thus, all of the concentrations of the six kinds of pathogenic bacteria both in PBS and liquorice extract showed an obvious negative linear correlation with the Raman intensity of SERS tag in the range of 10-10 7  CFU/mL with detection limits were all lower than 10 CFU/mL. And there was no significant difference between our method and the plate counting method. Besides, the assembled-aptasensor had superior specific recognition ability even in the mixed interfering bacteria. Our study showed that this assembled-aptasensor had good specific detection ability to a variety of foodborne pathogens based on magnetic field-assisted SERS technique, which can be used for rapid and sensitive detection of a variety of pathogens in complex substrates., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

A ratiometric electrochemical immunosensor is proposed for simultaneous detection of cellular-myelocytomatosis oncoprotein (C-myc) and B-cell lymphoma 2 (Bcl-2) via the potential-resolved strategy. It relied on multi-role co-loaded alloy composites (CLACs) and poly(3,4-ethylenedioxythiophene) (PEDOT)-graphene oxide (GO)-multiwalled carbon nanotubes (MWCNTs) (PGM) modified electrodes. CLACs with good catalytic and enzyme-like properties were synthesized in one step by loading tetramethylbenzidine (TMB) or methylene blue (MB) into Pt-Pd alloy and used as label materials. After immunological reactions, CLACs showed distinguishable dual differential pulse voltammetry signals at  - 0.26 V and 0.38 V, corresponding to C-myc and Bcl-2, and the PGM had an electrochemical signal at 1.2 V, which could be used as a reference signal to construct a ratiometric sensor. CLACs had a satisfactory synergistic effect with the PGM, and eventually achieved quadruple signal amplification. Thus, benefiting from multiple magnification and ratiometric self-calibration functions, sensitive detections of C-myc and Bcl-2 were achieved, with detection limits as low as 0.5 and 2.5 pg mL -1 , respectively. Additionally, when the designed method was applied to blood samples from lymphoma patients, results consistent with the ELISA kit were obtained. This will open avenues for constructing multiple protein detection sensors., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Alpha-fetoprotein (AFP) is inextricably linked to various diseases, including liver cancer. Thus, detecting the content of AFP in biology has great significance in diagnosis, treatment, and intervention. Motivated by the urgent need for affordable and convenient electronic sensors in the analysis and detection of aqueous biological samples, we combined the solution-gated graphene transistor (SGGT) with the catalytic reaction of enzyme nanoprobes (HRP-AuNPs-Ab2) to accurately sense AFP. The SGGT immunosensor demonstrated high specificity and stability, excellent selectivity, and excessive linearity over a range of 4 ng/mL to 500 ng/mL, with the lower detection limit down to 1.03 ng/mL. Finally, clinical samples were successfully detected by the SGGT immunosensor, and the results were consistent with chemiluminescence methods that are popular in hospitals for detecting AFP. Notably, the SGGT immunosensor is also recyclable, so it has excellent potential for use in high-throughput detection., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Fibrinogen as a major inflammation marker and blood coagulation factor has a direct impact on the health of humanity. The variations in fibrinogen content lead to risky conditions such as bleeding and cardiovascular diseases. So, accurate methods for monitoring of this glycoprotein are of high importance. The conventional methods, such as the Clauss method, are time consuming and require highly specialized expert analysts. The development of fast, simple, easy to use, and inexpensive methods is highly desired. In this way, biosensors have gained outstanding attention since they offer means for performing analyses at the points-of-care using self-testing devices, which can be applied outside of clinical laboratories or hospital. This review indicates that different electrochemical and optical sensors have been successfully implemented for the detection of fibrinogen under normal levels of fibrinogen in plasma. The biosensors for the detection of fibrinogen have been designed based on the quartz crystal microbalance, field-effect transistor, electrochemical impedance spectroscopy, amperometry, surface plasmon resonance, localized surface plasmon resonance, and colorimetric techniques. Also, this review demonstrates the utility of the application of nanoparticles in different detection techniques., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

A novel deep learning-enabled smartphone platform is developed to assist a colorimetric aptamer biosensor for fast and highly sensitive detection of dimethoate. The colorimetric determination of dimethoate is based on the specific binding of dimethoate and aptamer, which leads to the aggregation of AuNPs in high-concentration NaCl solution, resulting in an obvious color change from red to blue. This color change provides sufficient data for self-learning enabled by a convolutional neural network (CNN) model, which is established to predict dimethoate concentration based on images acquired from a smartphone. To enhance user-friendliness for non-experts, the CNN model is then embedded into a smartphone app, enabling offline detection of dimethoate pesticide in real environments within just 15 min using a pre-configured colorimetric probe. The developed platform exhibits superior performance, achieving a regression coefficient of 0.9992 in the concentration range of 0-10 μM. Moreover, the app's performance is found to be consistent with the ELISA kit. These remarkable findings demonstrate the potential of combining colorimetric biosensors with smartphone-based deep learning methods for the development of portable and affordable tools for pesticide detection., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

An ultrasensitive electrochemical biosensing platform has been designed by combining electrocatalysis-assisted H 2 S amplification with a chemical reaction-mediated electrochemical signal-boosted system for H 2 S detection based on Cu-Mn(OH) 2 hexagonal nanorings. The signal amplification is initiated by an electrocatalysis reaction that can grasp specific H 2 S substrates and further highly amplify electrochemical signals. Then, the unique chemical reaction is powered by copper ion and generates a large amount of electroactive Cu x S products on the electrode surface, thus achieving the multiple amplification of H 2 S detection. Finally, the Cu-Mn(OH) 2 loaded with plenty of electroactive Cu x S can be captured on the electrode for further improving the electrochemical signal thus obtaining ultra-high sensitive determination of H 2 S. The established electrochemical biosensing platform displays a wide analytical range of 0.1 μM to 265 μM with a low detection limit of 0.096 μM. The satisfactory selectivity allows the electrochemical sensor to distinguish H 2 S from other interfering substances without any complicated pretreatment, even in complex tumor cell samples. Thus, our designed electrocatalysis-assisted amplification strategy offers a powerful analysis toolkit for the early determination of H 2 S-related disease in clinical diagnosis., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Rod-like graphite carbon nitride@MnO 2 (R-g-C 3 N 5 @MnO 2 ) heterostructure was prepared by in situ self-anchored growth of MnO 2 nanosheet on the surface of R-g-C 3 N 5 . The synthesized R-g-C 3 N 5 @MnO 2 heterostructure as photoactive material exhibited excellent photoelectrochemical (PEC) performance, and the prepared heterostructure-aptamer probe displayed sensitive PEC response to cTnI. Therefore, the PEC method was developed to detect cTnI based on the R-g-C 3 N 5 @MnO 2 heterostructure. It was found that the linear response to cTnI was in the range 0.001-30 ng/mL under optimized conditions, and the detection limit of the proposed sensor was 0.3 pg/mL. The PEC method displays stable photocurrent response up to 8 cycles and exhibited outstanding selectivity and sensitivity. The PEC method was successfully applied to detect cTnI in serum samples. The recoveries of cTnI detection in serums reach 95.5-104%, and the relative standard deviations range from 3.20 to 4.45%., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The development of disease detection by biosensors represents one of the key components of medical science. However, millions of people are still misdiagnosed each year due to the poor efficacy and thermal instability of biosensors. Using horseradish peroxidase (HRP) as a paradigm, we offer a rational design strategy to optimize the thermostability and activity of biosensors by biomimetic mineralization. To overcome the weak thermostability of the biosensor, the mineralization of Fe-MOF forms an armor on HRP that protects against high temperature. Additionally, the biomimetic mineralization HRP@Fe-MOF can double-catalyze the TMB/H 2 O 2 chromogenic system for color development. The biosensor can also be recycled through simple heat treatment due to the thermally stable aptamer and biomimetic mineralization HRP@Fe-MOF. The optical biosensor based on this sensitive spectral transformation was successfully developed for the measurement of AβO with an outstanding linear range (0.0001-10 nM) and a low limit of detection (LOD) of 0.03 pM. This promising platform will open up new avenues for the detection of AβO in the early diagnosis of Alzheimer's disease (AD)., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

The aim of the current research is to design alcohol oxidase-based amperometric biosensors (ABSs) using hybrid metallic nanoparticles as artificial peroxidases (PO) or PO-like nanozymes (NZs). A lot of metallic PO-like NZs were synthesized and tested with respect to their ability to substitute natural PO in solution and on amperometric electrode. The most effective PO mimetics were coupled with alcohol oxidase (AOX) on graphite electrodes (GEs) and characterized. Two types of modified GEs, namely, the AOX/nAuCePt/GE and the AOX/nFePtAu/GE show the highest sensitivities to ethanol (2600 A⋅M -1 ⋅m -2 and 1250 A⋅M -1 ⋅m -2 , respectively), low limits of detection (1.5 µM and 2.2 µM), broad linear ranges (5 - 100 µM and 12 - 120 µM), as well as satisfactory storage stabilities. The most sensitive bioelectrode AOX/nAuCePt/GE was used as ABS for ethanol determination in real samples. The practical feasibility of the constructed ABS was demonstrated by determination of ethanol in beverages, human blood and saliva., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The epidemic of infectious diseases caused by contagious pathogens is a life-threatening hazard to the entire human population worldwide. A timely and accurate diagnosis is the critical link in the fight against infectious diseases. Aptamer-based biosensors, the so-called aptasensors, employ nucleic acid aptamers as bio-receptors for the recognition of target pathogens of interest. This review focuses on the design strategies as well as state-of-the-art technologies of aptasensor-based diagnostics for infectious pathogens (mainly bacteria and viruses), covering the utilization of three major signal transducers, the employment of aptamers as recognition moieties, the construction of versatile biosensing platforms (mostly micro and nanomaterial-based), innovated reporting mechanisms, and signal enhancement approaches. Advanced point-of-care testing (POCT) for infectious disease diagnostics are also discussed highlighting some representative ready-to-use devices to address the urgent needs of currently prevalent coronavirus disease 2019 (COVID-19). Pressing issues in aptamer-based technology and some future perspectives of aptasensors are provided for the implementation of aptasensor-based diagnostics into practical application., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The cornerstone of nanomaterial-based sensing systems is the synthesis of nanoparticles with appropriate surface functionalization that ensures their stability and determines their reactivity with organic or inorganic analytes. To accomplish these requirements, various compounds are used as additives or growth factors to regulate the properties of the synthesized nanoparticles and their reactivity with the target analytes. A different rationale is to use the target analytes as additives or growth agents to control the formation and properties of nanoparticles. The main difference is that the analyte recognition event occurs before or during the formation of nanoparticles and it is based on the reactivity of the analytes with the precursor materials of the nanoparticles (e.g., metal ions, reducing agents, and coatings). The transition from the ionic (or molecular) state of the precursor materials to ordered nanostructured assemblies is used for sensing and signal transduction for the qualitative detection and the quantitative determination of the target analytes, respectively. This review focuses on assays that are based on analyte-mediated regulation of nanoparticles' formation and differentiate them from standard nanoparticle-based assays which rely on pre-synthesized nanoparticles. Firstly, the principles of analyte-mediated nanomaterial sensors are described and then they are discussed with emphasis on the sensing strategies, the signal transduction mechanisms, and their applications. Finally, the main advantages, as well as the limitations of this approach, are discussed and compared with assays that rely on pre-synthesized nanoparticles in order to highlight the major advances accomplished with this type of nano-sensors and elucidate challenges and opportunities for further evolving new nano-sensing strategies., (© 2022. The Author(s).)

Achieving the early diagnosis of breast cancer, through ultrasensitive detection of tumor marker miRNA-155, is a significant challenge. Therefore, an ultrasensitive hairpin electrochemical biosensor based on graphite-like phase carbon nitride composite was proposed. In this paper, poly(D-glucosamine) (PDG) was used as a stabilizer and reducing agent to prepare gold nanoparticles at room temperature, and then a graphite-like phase with a two-dimensional lamellar structure carbon nitride was further combined with it to obtain the poly(D-glucosamine)/gold nanoparticles/graphite-like phase carbon nitride nanocomposite (PDG/AuNPs/g-C 3 N 4 ), in order to achieve the goal of signal amplification. The specific hairpin capture probe (HP) that recognized and bound miRNA-155 was then grafted. The hairpin biosensor showed a linear range of 0.1 fM-1 pM with a detection limit of 0.05 fM using differential pulse voltammetry (DPV) electrochemical analysis. Furthermore, the excellent performance hairpin electrochemical biosensor had been applied to the detection of miRNA-155 in human serum samples with good recovery., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

The outbreak rate of human coronaviruses (CoVs) especially highly pathogenic CoVs is increasing alarmingly. Early detection of these viruses allows treatment interventions to be provided more quickly to people at higher risk, as well as helping to identify asymptomatic carriers and isolate them as quickly as possible, thus preventing the disease transmission chain. The current diagnostic methods such as RT-PCR are not ideal due to high cost, low accuracy, low speed, and probability of false results. Therefore, a reliable and accurate method for the detection of CoVs in biofluids can become a front-line tool in order to deal with the spread of these deadly viruses. Currently, the nanomaterial-based sensing devices for detection of human coronaviruses from laboratory diagnosis to point-of-care (PoC) diagnosis are progressing rapidly. Gold nanoparticles (AuNPs) have revolutionized the field of biosensors because of the outstanding optical and electrochemical properties. In this review paper, a detailed overview of AuNP-based biosensing strategies with the varied transducers (electrochemical, optical, etc.) and also different biomarkers (protein antigens and nucleic acids) was presented for the detection of human coronaviruses including SARS-CoV-2, SARS-CoV-1, and MERS-CoV and lowly pathogenic CoVs. The present review highlights the newest trends in the SARS-CoV-2 nanobiosensors from the beginning of the COVID-19 epidemic until 2022. We hope that the presented examples in this review paper convince readers that AuNPs are a suitable platform for the designing of biosensors., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

MXene@Au as the base and Au@SiO 2 as signal amplification factor were used for constructing an ultrasensitive "on-off" electrochemiluminescence (ECL) biosensor for the detection of Pb 2+ in water. The use of MXene@Au composite provided a good interface environment for the loading of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+ ) on the electrode. Based on resonance energy transfer, the Au (core) SiO 2 (shell) (Au@SiO 2 ) nanoparticles stimulate electron transport and promote tripropylamine (TPrA) oxidation. The luminescence effect of Au@SiO 2 was five times that of AuNPs and SiO 2 nanomaterials alone, and the ECL intensity was greatly improved. In addition, Pb 2+ activated the aptamer to exert its endonuclease activity, which realized the signal cycle amplification in the process of Pb 2+ detection. When Pb 2+ was added, the ECL signal weakened, and the Pb 2+ concentration was detected according to the decreased ECL intensity. Under optimized experimental conditions, this aptamer sensor for Pb 2+ has a wide detection range (0.1 to 1 × 10 6  ng L -1 ) and a low detection limit (0.059 ng L -1 ). The relative standard deviation (RSD) of the sensor is 0.39-0.99%, and the recovery of spiked standard is between 90.00 and 125.70%. The sensor shows good selectivity and high sensitivity in actual water sample analysis. This signal amplification strategy possibly provides a new method for the detection of other heavy metal ions and small molecules., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Wavelength interrogation surface plasmon resonance imaging (WSPRi) sensing has unique advantages in high-throughput imaging detection. The refractive index resolution (RIR) of WSPRi is limited to the order of 10 -6 RIU. This paper demonstrates a novel WSPRi sensing system with a wavelength scanning device of an acousto-optic tunable filter (AOTF) and a low-cost speckle-free SPR excitation source of a halogen lamp. We developed a sensitive quasi-phase extraction method for data processing. The new technique achieved an RIR of 8.84×10 -7 RIU, which is the first WSPRi system that has an RIR in the order of 10 -7 RIU. Moreover, we performed a real-time recording of the formation of the coffee ring effect during brine evaporation and enhanced the biosensor performance of SPR for the first time. We believe the higher RIR and accuracy of the system will benefit more potential applications toward exploring the biomolecules' behaviors in biological and biochemistry studies., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

A new electrochemiluminescence (ECL) cytosensor is proposed for the simultaneous determination of phosphatidylserine (PS) and epidermal growth factor receptor (EGFR) based on the ECL signals of metal-organic framework-5 (MOF-5) loaded CdS quantum dots and N-(aminobutyl)-N-(ethylisoluminol)-polyethylenimine capped Au and Ag nanoparticles. Apoptosis promotes the exposure of PS and reduces the expression of EGFR in cell membranes. Two spatially resolved areas on dual-disk glassy carbon electrodes were designed to eliminate the interference from different ECL probes. Using HepG2 cells treated with resveratrol to induce apoptosis, the cytosensor exhibited high sensitivity, simplicity, and high reproducibility, demonstrating its potential in drug screening and rapid apoptotic cell detection. The strategy reported provides a promising platform for the highly sensitive cytosensing and convenient screening of clinically relevant anticancer drugs., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)