Hydrogel-Involved Colorimetric Platforms Based on Layered Double Oxide Nanozymes for Point-of-Care Detection of Liver-Related Biomarkers

Hydrogel-involved portable colorimetric sensor based on oxidase mimic Fe/Co-NC for acetylcholinesterase detection and pesticides inhibition assessment

Herein, we synthesized a novel N-doped carbon layer encapsulated Fe/Co bimetallic nanoparticles (Fe/Co-NC), which exhibited superior oxidase-like activity due to the facilitation of electron penetration and the formation of metal-nitrogen active sites. Fe/Co-NC could catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) to blue oxTMB. Acetylcholinesterase (AChE) could catalyze the hydrolysis of thioacetylcholine to produce reducing thiocholine, which prevented TMB from oxidation. Thus, a portable hydrogel colorimetric sensor was developed for on-site and visual monitoring of AChE with the detection limit of 0.36 U L-1, and successfully applied to detect AChE in human erythrocyte samples. Furthermore, this platform was used to investigate the inhibition of triazophos on AChE activity.

FeMo2Ox(OH)y-based mineral hydrogels as a novel POD nanozyme for sensitive and selective detection of aromatic amines contaminants via a colorimetric sensor array

Developing convenient pathways to discriminate and identify multiple aromatic amines (AAs) remains fascinating and critical. Here, a novel three-channel colorimetric sensor array based on FeMo2Ox(OH)y-based mineral (FM) hydrogels is successfully constructed to monitor AAs in tap water. Benefiting from the substantial oxygen vacancies (VO), FM nanozymes exhibit extraordinary peroxidase (POD)-like activities with Km of 0.133 mM and Vmax of 2.518 × 10-2 mM·s-1 toward 3,3',5,5'-tetramethylbenzidine (TMB), which are much better than horseradish peroxidase and most of POD mimics. This reveals that doping Cu and Co into FM (FM-Cu and FM-Co) can change POD activity. Based on various POD activities, TMB and H2O2 are used to generate fingerprint colorimetry signals from the colorimetry sensor array. The analytes can accurately discriminate through linear discriminant analysis, with a detection limit as low as 2.12 × 10-2-0.14 μM. The sensor array can effectively identify and discriminate AA contaminants and their mixtures and has performed well in real sample tests.

The Nanozyme Revolution: Enhancing the Performance of Medical Biosensing Platforms

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with "gold-standard" techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

A point-of-care solid-phase colorimetric sensor based on the enzyme-induced metallization for ALP detection

Alkaline phosphatase (ALP) is a crucial biomarker for clinical diagnosis, which is closely related to the physiological homeostasis regulation process of human body. And the abnormal level of ALP is associated with numerous diseases, such as liver dysfunction, bone diseases, diabetes, and so on. In order to meet the demand of personalized healthcare, it is particularly important to develop a miniaturized point-of-care testing (POCT) device for ALP detection. Herein, a portable solid-phase colorimetric sensor based on enzyme-induced metallization signal amplification strategy was constructed for ALP detection. The AuNPs modified on the glass slides acted as crystal seeds, allowing Ag+ in the solution to be reduced and deposited on the surface of AuNPs, which further formed the gold core and silver shell (Au@Ag) complex and generated visual signals. The visual signals were recorded by a smartphone and quantified using open-source ImageJ software. Under the optimal conditions, the proposed method exhibited a good linear relationship from 2.0 to 16.0 pM, and the detection limit was as low as 0.9 pM. In addition, it was further successfully applied for ALP detection in non-transparent and complex samples (milk, different types of cells). A sensitive, low cost, rapid and convenient solid-phase sensor was developed for ALP detection, which was expected to provide a promising strategy for POCT devices.

A specific visual-volumetric sensor for mercury ions based on smart hydrogel

On the basis of the "seeing is believing" concept and the existing theory of Hg2+ coordination chemistry, for the first time, we innovatively designed and synthesized a visual-volumetric sensor platform with fluorescein and uracil functionalized polyacrylamide hydrogel. Without the aid of any complicated instruments and power sources, the sensor-enabled quantitative μM-level Hg2+ detection Hg2+ by reading graduation on a pipette with the naked eye. The sensor undergoes volumetric response and shows a wide linear response range to Hg2+ (1.0 × 10-6-5.0 × 10-5 mol L-1) with 2.8 × 10-7 mol L-1 as the detection limit. The highly selective (easily distinguished Hg2+ from other common metal ions), rapid response (∼30 min), and acceptable repeatability (RSD < 5% in all cases) demonstrated that the developed sensor is suitable for onsite practical use for the determination of Hg2+ while being low-cost, simple, and portable. The design principles of the obtained materials and the construction techniques and methods of the sensors described in our study provide a new idea for the research and development of smart materials and a series of visual-volumetric sensors for other analytes.

Signal Amplification Strategy Design in Nanozyme-Based Biosensors for Highly Sensitive Detection of Trace Biomarkers

Nanozymes show great promise in enhancing disease biomarker sensing by leveraging their physicochemical properties and enzymatic activities. These qualities facilitate signal amplification and matrix effects reduction, thus boosting biomarker sensing performance. In this review, recent studies from the last five years, concentrating on disease biomarker detection improvement through nanozyme-based biosensing are examined. This enhancement primarily involves the modulations of the size, morphology, doping, modification, electromagnetic mechanisms, electron conduction efficiency, and surface plasmon resonance effects of nanozymes for increased sensitivity. In addition, a comprehensive description of the synthesis and tuning strategies employed for nanozymes has been provided. This includes a detailed elucidation of their catalytic mechanisms in alignment with the fundamental principles of enhanced sensing technology, accompanied by the presentation of quantitatively analyzed results. Moreover, the diverse applications of nanozymes in strip sensing, colorimetric sensing, electrochemical sensing, and surface-enhanced Raman scattering have been outlined. Additionally, the limitations, challenges, and corresponding recommendations concerning the application of nanozymes in biosensing have been summarized. Furthermore, insights have been offered into the future development and outlook of nanozymes for biosensing. This review aims to serve not only as a reference for enhancing the sensitivity of nanozyme-based biosensors but also as a catalyst for exploring nanozyme properties and their broader applications in biosensing.

Self-template sacrifice and in situ oxidation of a constructed hollow MnO2 nanozymes for smartphone-assisted colorimetric detection of liver function biomarkers

Liver function tests play a vital role in accurately diagnosing liver diseases, monitoring treatment outcomes, and assessing liver damage severity. Here, we introduce a novel approach to develop a smartphone-assisted portable colorimetric sensor for rapid detection of three liver function biomarkers: aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP). This sensor is based on the inherent enzyme-like activities of hollow MnO2 (H-MnO2). The H-MnO2 is synthesized via a self-template sacrifice and in situ oxidation strategy, utilizing a manganese-based Prussian blue analogue (Mn-PBA) as a sacrificial template. The resulting H-MnO2 exhibits a polycrystalline structure with a large specific surface area. By encapsulating the H-MnO2 in sodium alginate, we construct a portable sensing platform facilitating specific and rapid colorimetric detection of the three liver function biomarkers with the assistance of a smartphone. The developed sensor demonstrates outstanding sensitivity and stability, achieving detection limits of 4.9 U L-1, 3.6 U L-1, and 0.99 U L-1 for AST, ALT, and ALP, respectively. Importantly, this work introduces an innovative in situ oxidation method for fabricating hollow nanozymes, offering a cost-effective and convenient assay for liver function biomarkers detection.

Determination of the Catalytic Activity of a Peroxidase-like Nanozyme and Differences among Layered Double Hydroxides with Different Anions and Cations

Nanomaterials with enzyme-like activity, namely, nanozymes, have been widely used as substitutes for natural enzymes, and they show excellent potential for application in many fields, such as biotechnology, environmental chemistry, and medicine. Layered double hydroxides (LDHs) are inorganic nanomaterials with adjustable compositions, simple preparation methods, and low costs and are some of the most promising candidate materials for the preparation of nanozymes. Here, we studied the syntheses and peroxidase-like activities of LDHs with four anions and four cations. First, LDHs prepared by the coprecipitation-hydrothermal method adopted hexagonal lamellar structures with good dispersion and uniform particle sizes. The Lambert-Beer law showed that the prepared LDHs exhibited good enzymatic activity. Later, the Km and Vmax values of the LDHs with different anionic/cationic materials intercalated into their structures were compared. Under the optimum conditions, the Vmax of Mg2Al-NO3-LDH was 7.35 × 10-2, which is 2-4 times higher than that of the LDHs containing other anions; the Vmax values of NiFe-LDH and FeAl-LDH were 0.152 and 0.284, respectively, which are 10 times higher than those of the LDHs with other cations. Importantly, according to kinetic analyses of the enzymatic reactions, the effects of Fe2+ and Fe3+ on the LDH enzyme activity were greater than those of the intercalated anions. This study showed that NiFe-LDH and FeAl-LDH with high catalytic activities are candidate materials for peroxidase simulations, which may provide new strategies for the application of LDHs in biosensors, antioxidants, biotechnology, and other nanozyme applications.

Fe(III)-incorporated porphyrin-based conjugated organic polymer as a peroxidase mimic for the sensitive determination of glucose and H2O2

Nanozymes, i.e., nanomaterials that possess intrinsic enzyme-like behaviour, have thrived over the past few decades owing to their advantages of superior stability and effortless storage. Such artificial enzymes can be a perfect alternative to naturally occurring enzymes, which have disadvantages of high cost and limited functionality. In this work, we present the fabrication of an Fe(III)-incorporated porphyrin-based conjugated organic polymer as a nanozyme for the efficient detection of glucose through its intrinsic peroxidase activity and the amperometric detection of hydrogen peroxide. The iron-incorporated porphyrin-based conjugated organic polymer (Fe-DMP-POR) possesses a spherical morphology with high chemical and thermal stability. Exploiting the peroxidase-mimicking activity of the material for the determination of glucose, a detection limit of 4.84 μM is achieved with a linear range of 0-0.15 mM. The Fe-DMP-POR also exhibits a reasonable recovery range for the detection of human blood glucose. The as-synthesized material can also act as an H2O2 sensor, with a sensitivity of 947.67 μA cm-2 mM-1 and a limit of detection of 3.16 μM.

Low-Cost Point-of-Care Monitoring of ALT and AST Is Promising for Faster Decision Making and Diagnosis of Acute Liver Injury

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are important liver enzymes in clinical settings. Their levels are known to be elevated in individuals with underlying liver diseases and those consuming hepatotoxic drugs. Serum ALT and AST levels are crucial for diagnosing and assessing liver diseases. Serum ALT is considered the most reliable and specific candidate as a disease biomarker for liver diseases. ALT and AST levels are routinely analyzed in high-risk individuals for the bioanalysis of both liver function and complications associated with drug-induced liver injury. Typically, ALT and AST require blood sampling, serum separation, and testing. Traditional methods require expensive or sophisticated equipment and trained specialists, which is often time-consuming. Therefore, developing countries have limited or no access to these methods. To address the above issues, we hypothesize that low-cost biosensing methods (paper-based assays) can be applied to the analysis of ALT and AST levels in biological fluids. The paper-based biodetection technique can semi-quantitatively measure ALT and AST from capillary finger sticks, and it will pave the way for the development of an inexpensive and rapid alternative method for the early detection and diagnosis of liver diseases. This method is expected to significantly reduce the economic burden and aid routine clinical analysis in both developed and underdeveloped countries. The development of low-cost testing platforms and their diagnostic utility will be extremely beneficial in helping millions of patients with liver disorders.

Microfluidic Devices: A Tool for Nanoparticle Synthesis and Performance Evaluation

The use of nanoparticles (NPs) in nanomedicine holds great promise for the treatment of diseases for which conventional therapies present serious limitations. Additionally, NPs can drastically improve early diagnosis and follow-up of many disorders. However, to harness their full capabilities, they must be precisely designed, produced, and tested in relevant models. Microfluidic systems can simulate dynamic fluid flows, gradients, specific microenvironments, and multiorgan complexes, providing an efficient and cost-effective approach for both NPs synthesis and screening. Microfluidic technologies allow for the synthesis of NPs under controlled conditions, enhancing batch-to-batch reproducibility. Moreover, due to the versatility of microfluidic devices, it is possible to generate and customize endless platforms for rapid and efficient in vitro and in vivo screening of NPs' performance. Indeed, microfluidic devices show great potential as advanced systems for small organism manipulation and immobilization. In this review, first we summarize the major microfluidic platforms that allow for controlled NPs synthesis. Next, we will discuss the most innovative microfluidic platforms that enable mimicking in vitro environments as well as give insights into organism-on-a-chip and their promising application for NPs screening. We conclude this review with a critical assessment of the current challenges and possible future directions of microfluidic systems in NPs synthesis and screening to impact the field of nanomedicine.

A Nitro Functionalized MOF with Multi-Enzyme Mimetic Activities for the Colorimetric Sensing of Glucose at Neutral pH

Benefiting from the advantages like large surface area, flexible constitution, and diverse structure, metal-organic frameworks (MOFs) have been one of the most ideal candidates for nanozymes. In this study, a nitro-functionalized MOF, namely NO₂-MIL-53(Cu), was synthesized. Multi-enzyme mimetic activities were discovered on this MOF, including peroxidase-like, oxidase-like, and laccase-like activity. Compared to the non-functional counterpart (MIL-53(Cu)), NO₂-MIL-53(Cu) displayed superior enzyme mimetic activities, indicating a positive role of the nitro group in the MOF. Subsequently, the effects of reaction conditions on enzyme mimetic activities were investigated. Remarkably, NO₂-MIL-53(Cu) exhibited excellent peroxidase-like activity even at neutral pH. Based on this finding, a simple colorimetric sensing platform was developed for the detection of H₂O₂ and glucose, respectively. The detection liner range for H₂O₂ is 1-800 μM with a detection limit of 0.69 μM. The detection liner range for glucose is linear range 0.5-300 μM with a detection limit of 2.6 μM. Therefore, this work not only provides an applicable colorimetric platform for glucose detection in a physiological environment, but also offers guidance for the rational design of efficient nanozymes with multi-enzyme mimetic activities.

Aptasensors Are Conjectured as Promising ALT and AST Diagnostic Tools for the Early Diagnosis of Acute Liver Injury

Abnormal levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in human serum are the most sensitive indicator of hepatocellular damage. Because liver-related health problems are directly linked to elevated levels of ALT and AST, it is important to develop accurate and rapid methods to detect these enzymes for the early diagnosis of liver disease and prevention of long-term liver damage. Several analytical methods have been developed for the detection of ALT and AST. However, these methods are based on complex mechanisms and require bulky instruments and laboratories, making them unsuitable for point-of-care application or in-house testing. Lateral flow assay (LFA)-based biosensors, on the other hand, provide rapid, accurate, and reliable results, are easy to operate, and are affordable for low-income populations. However, due to the storage, stability, batch-to-batch variations, and error margins, antibody-based LFAs are considered unaffordable for field applications. In this hypothesis, we propose the selection of aptamers with high affinity and specificity for the liver biomarkers ALT and AST to build an efficient LFA device for point-of-care applications. Though the aptamer-based LFA would be semiquantitative for ALT and AST, it would be an inexpensive option for the early detection and diagnosis of liver disease. Aptamer-based LFA is anticipated to minimize the economic burden. It can also be used for routine liver function tests regardless of the economic situation in each country. By developing a low-cost testing platform, millions of patients suffering from liver disease can be saved.

A three-in-one hybrid nanozyme for sensitive colorimetric biosensing of pathogens

Pathogen screening is an important step in preventing foodborne diseases. In this study, a hybrid nanozyme, metal organic framework decorated with palladium (Pd) and platinum (Pt) (MIL-88@Pd/Pt), was innovatively synthesized and used with immune magnetic nanobeads (MNBs) for sensitive biosensing of Salmonella. First, immune MIL-88@Pd/Pt nanozymes and immune MNBs were mixed with target pathogens in a large-volume sample, resulting in effective isolation and specific label of target pathogens to form nanobead-Salmonella-nanozyme conjugates. Then, these conjugates were used to catalyze H₂O₂-TMB, and its color was changed from colorless to blue. Finally, catalysate absorption was measured to determine pathogen concentration. This colorimetric immunoassay could determine Salmonella typhimurium from 4 × 10¹ to 4 × 10⁵ CFU/mL in 60 min with a detection limit of 32 CFU/mL.

Cu2+ assisted carnation-like fluorescent metal-organic framework for triple-mode detection of glyphosate in food samples

Herein, by employing a novel synthesized ligand H₂L, a flower-like luminescent metal-organic framework IRMOF-3-L was constructed for developing a triple-mode sensor for glyphosate (Glyp) detection. The ligand H₂L was designed to contain three functional parts, which endowed the resulted IRMOF-3-L with peroxidase-like activity and unique fluorescence property, as well as specific combining capacity for Cu²⁺ to quench its fluorescence. The quenched fluorescence of IRMOF-3-L/Cu²⁺ could be recovered by Glyp to realize fluorescence detection of Glyp. Besides, the peroxidase activity of IRMOF-3-L/Cu²⁺ could also be inhibited by Glyp, and result in the decrease of catalysate oxTMB, concurrently reducing the changes of colorimetric and SERS signal. Therefore, the fluorescent/colorimetric/SERS triple-mode based detection of Glyp was favorably realized, and the detection limits were calculated as low as 0.738, 2.26 and 0.186 nM, respectively. Furthermore, a portable test strips-smartphone sensing platform was constructed for point of care testing of Glyp in food samples.

Nanozymes towards Personalized Diagnostics: A Recent Progress in Biosensing

This review highlights the recent advancements in the field of nanozymes and their applications in the development of point-of-care biosensors. The use of nanozymes as enzyme-mimicking components in biosensing systems has led to improved performance and miniaturization of these sensors. The unique properties of nanozymes, such as high stability, robustness, and surface tunability, make them an attractive alternative to traditional enzymes in biosensing applications. Researchers have explored a wide range of nanomaterials, including metals, metal oxides, and metal-organic frameworks, for the development of nanozyme-based biosensors. Different sensing strategies, such as colorimetric, fluorescent, electrochemical and SERS, have been implemented using nanozymes as signal-producing components. Despite the numerous advantages, there are also challenges associated with nanozyme-based biosensors, including stability and specificity, which need to be addressed for their wider applications. The future of nanozyme-based biosensors looks promising, with the potential to bring a paradigm shift in biomolecular sensing. The development of highly specific, multi-enzyme mimicking nanozymes could lead to the creation of highly sensitive and low-biofouling biosensors. Integration of nanozymes into point-of-care diagnostics promises to revolutionize healthcare by improving patient outcomes and reducing costs while enhancing the accuracy and sensitivity of diagnostic tools.

Spherical Hydrogel Sensor Based on PB@Fe-COF@Au Nanoparticles with Triplet Peroxidase-like Activity and Multiple Capture Sites for Effective Detection of Organophosphorus Pesticides

The residues of organophosphorus pesticides (OPs) have drawn worldwide increasing attention because of their potential fatal effects on human health and ecological systems. It is of great significance to develop an efficient and portable method for in-field detection of OPs. Herein, a novel core-shell nanocomposite of prussian blue@Fe-covalent organic framework@Au (PB@Fe-COF@Au) was constructed. Fe²⁺ and Fe³⁺ in PB nanoparticle (PBNP) cores, Fe-porphyrin in COF shells, and AuNPs grown on shells all acted as peroxidase-like catalytic active sites, enabling PB@Fe-COF@Au to possess triplet peroxidase-like activity. A colorimetric, affordable, sensitive, and selective strategy was designed to detect OPs. Compared with previous reports, this sensor realized a wider linear range for chlorpyrifos of 10-800 ng mL^-1 with a relatively lower detection limit of 0.61 ng mL^-1, which was attributed to the overlapping triple catalytic sites of PB@Fe-COF@Au and triple response sites to OPs. The assay was successfully employed to detect chlorpyrifos in food and environmental samples. Moreover, to meet the demand of in-field detection for OPs, a spherical hydrogel method based on PB@Fe-COF@Au with visual, portable, and equipment-free features was fabricated. This work provides a new pathway to design and apply effective nanozymes for on-site monitoring of pesticides.

A turn-on fluorescent strategy for alkaline phosphatase detection based on enzyme-assisted signal amplification

As a representative biochemical indicator, alkaline phosphatase (ALP) is of great importance in indicating and diagnosing clinical diseases. Herein, we developed a signal-on fluorescence sensing method for sensitive ALP activity detection based on the enzyme-assisted target recycling (EATR) technique. In this method, a two-step signal amplification process is designed. In the presence of ALP, the 3' phosphate group of an ss-DNA is removed explicitly by ALP, thus releasing free 3'-OH. Terminal deoxynucleotidyl transferase (TdT) can subsequently extend this substrate to generate poly(A) tails, converting the trace-level ALP information into multiple sequences and achieving the first-time amplification. A poly(T) Taqman probe labeled with FAM and BHQ1 provides the second one under the assistance of T7 exonuclease (T7 Exo) through alternate hybridization and degradation of ds-DNA regions. The previously quenched fluorescence is recovered due to the departure of FAM/BHQ1 during the cleavage of T7 Exo. Thus, taking advantage of template-free TdT-mediated polymerization and T7 Exo-based EATR, this strategy shows a sensitive LOD at 0.0074 U/L (S/N = 3) and a linear range of 0.01-8 U/L between ALP concentration and fluorescence intensity. To further verify the specificity and accuracy in practical application, we challenged it in a set of co-existing interference and biological environments and have gained satisfying results. The proposed method successfully quantified the ALP levels in clinical human serum samples, suggesting its applicability in practical application. Moreover, we have used this method to investigate the inhibition effects of Na₃VO₄. Above all, the proposed assay is sensitive, facile, and cost-effective for ALP determining, holding a promising perspective and excellent potential in clinical diagnosis and drug screening.

Smartphone-Facilitated Mobile Colorimetric Probes for Rapid Monitoring of Chemical Contaminations in Food: Advances and Outlook

Smartphone-derived colorimetric tools have the potential to revolutionize food safety control by enabling citizens to carry out monitoring assays. To realize this, it is of paramount significance to recognize recent study efforts and figure out important technology gaps in terms of food security. Driven by international connectivity and the extensive distribution of smartphones, along with their built-in probes and powerful computing abilities, smartphone-based sensors have shown enormous potential as cost-effective and portable diagnostic scaffolds for point-of-need tests. Meantime, the colorimetric technique is of particular notice because of its benefits of rapidity, simplicity, and high universality. In this study, we tried to outline various colorimetric platforms using smartphone technology, elucidate their principles, and explore their applications in detecting target analytes (pesticide residues, antibiotic residues, metal ions, pathogenic bacteria, toxins, and mycotoxins) considering their sensitivity and multiplexing capability. Challenges and desired future perspectives for cost-effective, accurate, reliable, and multi-functions smartphone-based colorimetric tools have also been debated.

Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex-Hemin Complex

Mercury ion (Hg²⁺) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS₂ photoanode of the split G-quadruplex-hemin complex, the magnetic NiCo₂O₄@SiO₂-NH₂ sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg²⁺ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo₂O₄@SiO₂-NH₂ and then partly hybridized with another single-stranded DNA2 (S2). When Hg²⁺ was present, the thymine-Hg²⁺-thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K⁺. After addition of hemin, the split G-quadruplex-hemin complex was obtained and effectually catalyzed the H₂O₂-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg²⁺. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex-hemin complex effectively switched the photocurrent polarity of SnS₂-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg²⁺ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg²⁺ in environmental fields.

Microwave-Assisted Synthesis of Sulfur Quantum Dots for Detection of Alkaline Phosphatase Activity

Sulfur quantum dots (SQDs) are a kind of pure elemental quantum dots, which are considered as potential green nanomaterials because they do not contain heavy metal elements and are friendly to biology and environment. In this paper, SQDs with size around 2 nm were synthesized by a microwave-assisted method using sulfur powder as precursor. The SQDs had the highest emission under the excitation of 380 nm and emit blue fluorescence at 470 nm. In addition, the SQDs had good water solubility and stability. Based on the synthesized SQDs, a fluorescence assay for detection of alkaline phosphatase (ALP) was reported. The fluorescence of the SQDs was initially quenched by Cr (VI). In the presence of ALP, ALP-catalyzed hydrolysis of 2-phospho-L-ascorbic acid to generate ascorbic acid. The generated ascorbic acid can reduce Cr (VI) to Cr (III), thus the fluorescence intensity of SQDs was restored. The assay has good sensitivity and selectivity and was applied to the detection of ALP in serum samples. The interesting properties of SQDs can find a wide range of applications in different sensing and imaging areas.

A Copper-Based Biosensor for Dual-Mode Glucose Detection

Glucose is a source of energy for daily activities of the human body and is regarded as a clinical biomarker, due to the abnormal glucose level in the blood leading to many endocrine metabolic diseases. Thus, it is indispensable to develop simple, accurate, and sensitive methods for glucose detection. However, the current methods mainly depend on natural enzymes, which are unstable, hard to prepare, and expensive, limiting the extensive applications in clinics. Herein, we propose a dual-mode Cu₂O nanoparticles (NPs) based biosensor for glucose analysis based on colorimetric assay and laser desorption/ionization mass spectrometry (LDI MS). Cu₂O NPs exhibited excellent peroxidase-like activity and served as a matrix for LDI MS analysis, achieving visual and accurate quantitative analysis of glucose in serum. Our proposed method possesses promising application values in clinical disease diagnostics and monitoring.