Detection of glutathione based on MnO2 nanosheet-gated mesoporous silica nanoparticles and target induced release of glucose measured with a portable glucose meter

Point-of-care testing of methotrexate using a controlled release sensor based on a personal glucose meter

Methotrexate (MTX), a widely administered medication for treating an array of tumors and autoimmune disorders, necessitates stringent monitoring due to the potential for severe adverse effects associated with its high dosage. Nevertheless, the existing methods for monitoring MTX are often intricate, time-consuming and incur significant costs. In this work, we constructed a controlled release sensor, harnessing the versatility of a personal glucose meter (PGM), which had been devised for the swift detection of MTX. This innovative approach employed HP-UiO-66-NH2 as a nanoscale reservoir for glucose encapsulation, with aptamer-conjugated gold nanoparticles (AuNPs@Apt) serving as molecular gates, sealing the pores of the nano-container. Upon the introduction of MTX into the solution, a specific recognition event occurred between the aptamer and MTX, leading to the formation of a stable AuNPs@Apt-MTX complex. This interaction triggered the release of AuNPs@Apt from the surface of HP-UiO-66-NH2, allowing glucose to escape, which was then detected by the PGM. This method demonstrated a robust linear response to MTX concentrations spanning from 0.1 μM to 20 μM, with a remarkable detection limit of 0.1 μM. Extensive experiments underscored the platform's exceptional selectivity for MTX detection, coupled with excellent reproducibility and stability, with a detection time of only 30 minutes. Importantly, it had been successfully applied to the analysis of MTX in diluted human serum with satisfactory recoveries. Given its portability and cost-effectiveness, this platform paved a novel avenue for monitoring MTX blood drug levels, offering significant potential for clinical applications and drug monitoring strategies.

AFB1-responsive mesoporous silica nanoparticles for AFB1 quantification based on aptamer-regulated release of SERS reporter

In this study, we propose a novel surface-enhanced Raman scattering (SERS) method for quantifying aflatoxin B1 (AFB1). This method relies on the target-triggered release of a SERS reporter from aptamer-sealed aminated mesoporous silica nanoparticles (MSNs). These MSNs were synthesized to accommodate 4-mercaptophenylboronic acid (4-MPBA) within their well-defined micropores, which were subsequently sealed with AFB1 aptamers. Upon specific binding of AFB1 to its aptamer, the conformational change in the aptamer is regulated by the presence of the target. Consequently, a positive linear relationship between the AFB1 concentration and the 4-MPBA SERS signal was observed. Under optimal conditions, the method exhibited a good linear relationship over the range of 0.1 to 5 ng/mL AFB1, with a limit of detection (LOD) of 0.03 ng/mL. This strategy was validated using wheat samples, yielding results comparable to high performance liquid chromatography-fluorescence detector (P > 0.05), confirming its reliability for detecting AFB1 in complex food matrices.

Portable Detection of Copper Ion Using Personal Glucose Meter

A simple and sensitive method for Cu2+ detection was developed using the Cu+-catalyzed alkyne-azide cycloaddition reaction, Fe3O4 magnetic nanoparticles (MNPs) as the reaction platform, and a portable blood glucose meter (PGM) as the detection method. Gold nanoparticles (AuNPs) were labeled with glucose oxidase (GOx) and alkyne-functionalized, terminally thiolated ssDNA (C2). In the presence of Cu2+ and ascorbate, the functionalized AuNPs were captured onto MNPs modified with azide-functionalized ssDNA (C1) via the Cu+-catalyzed alkyne-azide cycloaddition reaction. The GOx on the AuNPs' surface oxidized glucose (Glu) into gluconic acid and H2O2, reducing the Glu content in the reaction solution, which was quantitatively detected by the PGM. Under optimal conditions, the PGM response of the system showed a good linear relationship with the logarithm of Cu2+ concentration in the range of 0.05 to 10.00 μmol/L, with a detection limit of 0.03 μmol/L (3σ). In actual tap water samples, the spiked recovery rate of Cu2+ was between 92.30% and 113.33%, and the relative standard deviation was between 0.14% and 0.34%, meeting the detection requirements for Cu2+ in real water samples.

Recent advances on nanomaterial-based glutathione sensors

Glutathione (GSH) is one of the most common thiol-containing molecules discovered in biological systems, and it plays an important role in many cellular functions, where changes in physiological glutathione levels contribute to the progress of a variety of diseases. Molecular imaging employing fluorescent probes is thought to be a sensitive technique for online fluorescence detection of GSH. Although various molecular probes for (intracellular) GSH sensing have been reported, some aspects remain unanswered, such as quantitative intracellular analysis, dynamic monitoring, and compatibility with biological environment. Some of these drawbacks can be overcome by sensors based on nanostructured materials, that have attracted considerable attention owing to their exceptional properties, including a large surface area, heightened electro-catalytic activity, and robust mechanical resilience, for which they have become integral components in the development of highly sensitive chemo- and biosensors. Additionally, engineered nanomaterials have demonstrated significant promise in enhancing the precision of disease diagnosis and refining treatment specificity. The aim of this review is to investigate recent advancements in fabricated nanomaterials tailored for detecting GSH. Specifically, it examines various material categories, encompassing carbon, polymeric, quantum dots (QDs), covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal-based, and silicon-based nanomaterials, applied in the fabrication of chemo- and biosensors. The fabrication of nano-biosensors, mechanisms, and methodologies employed for GSH detection utilizing these fabricated nanomaterials will also be elucidated. Remarkably, there is a noticeable absence of existing reviews specifically dedicated to the nanomaterials for GSH detection since they are not comprehensive in the case of nano-fabrication, mechanisms and methodologies of detection, as well as applications in various biological environments. This research gap presents an opportune moment to thoroughly assess the potential of nanomaterial-based approaches in advancing GSH detection methodologies.

Mechanism underlying the effect of MnO2 nanosheets for A549 cell chemodynamic therapy

MnO2 nanosheets (MnO2NSs) were synthesized by one-step method, and MnO2NSs were applied to A549 cell chemodynamic Therapy (CDT). The cytotoxicity, redox ability, and reactive oxygen species production of MnO2NSs have been investigated, and differences in cell metabolism during CDT were determined using liquid chromatography-mass spectrometry (LC-MS/MS). In addition, the metabolites of A549 lung cancer cells affected by MnO2NSs treatment are identified; metabolite differences were identified by PCA, PLS-DA, orthogonal PLS-DA, and other methods; and these differences were analyzed using non-targeted metabolomics. We found that A549 cells which were treated by MnO2NSs have 17 different metabolites and 9 metabolic pathways that varied markedly. Owing to their unique composition, structure, and physicochemical properties, MnO2NSs and their composites have become a favored type of nanomaterial used for CDT in cancer therapy. This work provides insights into the mechanism underlying the effects of MnO2NSs on the tumor microenvironment of A549 lung cancer cells, effectively making up for the deficiency of the study on cellular mechanism of CDT-induced apoptosis of cancer cells. It could aid the development of cancer CDT treatment strategies and help improve the use of nanomaterials in the clinical field.

Metabolomics analysis of MnO2 nanosheets CDT for breast cancer cells and mechanism of cytotoxic action

Chemodynamic therapy (CDT) has received more and more attention as an emerging therapeutic strategy, especially transition metals with Fenton or Fenton-like activity have good effects in CDT research, manganese dioxide nanosheets (MnO2 NSs) and their complexes have become one of the most favored nanomaterials in CDT of tumors. CDT is mainly based on the role of reactive oxygen species (ROS) in tumor treatment, which have clear chemical properties and produce clear chemical reactions. However, their mechanism of interaction with cells has not been fully elucidated. Here, we performed CDT on mouse breast cancer cells (4T1) based on MnO2 NSs, extracted the metabolites from the 4T1 cells during the treatment, and analyzed the differences in metabolites by using high-resolution liquid chromatography-mass spectrometry (LC-MS). Untargeted metabolomics studies were conducted using the relevant data. This study mainly explored the changes in MnO2 NSs on the metabolite profile of 4T1 cells and their potential impact on tumor therapy, in order to determine the mechanism of action of MnO2 NSs in the treatment of breast cancer. The results of the study showed the presence of 11 different metabolites in MnO2 NSs CDT for 4T1 tumor cells, including phosphoserine, sphingine, phosphocholine, and stearoylcarnitine. These findings provide a deeper understanding of breast cancer treatment, and are beneficial for the further research and clinical application of CDT.

The development of a novel copper-loaded mesoporous silica nanoparticle as a peroxidase mimetic for colorimetric biosensing and its application in H2O2 and GSH assay

In recent years, the development of nanomaterials-based peroxidase mimics as enzyme sensors has been attracting considerable interest due to their outstanding features, including potent stability, and cost-effectiveness toward natural enzymes. In this work, mesoporous silica nanoparticles functionalized by copper (Cu-MSN) were prepared as a new artificial enzyme for the first time through the sol-gel procedure. A comprehensive investigation of the catalytic activity of Cu-MSN was done through the oxidation of chromogenic peroxidase substrates, 3,3',5,5'-tetramethylbenzidine (TMB), and (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), in the presence of H₂O₂. The results indicate that the peroxidase-like activity of the as-prepared sample is significantly higher than other nanoparticles. Additionally, for the study, a facile and rapid sensing method based on the enzyme-like activity of Cu-MSN to detect H₂O₂ and glutathione (GSH) was developed to examine the potency of the proposed biosensor. Preliminary analysis revealed that the limit of detection (LOD) of H₂O₂ and GSH is 0.2 and 0.0126 μM, in the range of 0.9-100 and 0.042-1 μM, respectively. These findings support the claims for the efficiency of the sensor in detection fields. Also, human serum was utilized as the real sample to obtain additional evidence.

In Situ Synthesis of Horseradish Peroxidase Nanoflower@Carbon Nanotube Hybrid Nanobiocatalysts with Greatly Enhanced Catalytic Activity

Organic-inorganic hybrid nanoflowers (NFs) consisting of horseradish peroxidase (HRP) and copper II (Cu2+) are successfully synthesized with the involvement of carbon nanotubes (CNTs) by in situ and post-modification methods. Catalytic activities of in situ synthesized HRP-NF@CNT (HRP-NF@CNT-Is) and post-modification-synthesized HRP-NF@CNTs (HRP-NF@CNT-Pm) are systematically examined. The 30 mg CNTs incorporated HRP-NF@CNT-Is (HRP-NF@CNT-30Is) exhibits greatly increased catalytic activity and stability toward 3,3',5,5'-tetramethylbenzidine (TMB), thanks to the synergistic effect between HRP-NF and CNTs and the peroxidase-like activity of CNTs in the presence of hydrogen peroxide (H2O2). While HRP-NF@CNT-30Is retains almost 85% of its initial activity even after 10 cycles, HRP-NF (without CNTs) loses half of its initial activity at the same experimental conditions. We study how two experimental parameters, the pH values and temperatures, influence the catalytic activity of HRP-NF@CNT-30Is, in addition to the fact that HRP-NF@CNT-30Is is employed to detect the presence of H2O2 and glutathione (GSH) with colorimetric and spectrophotometric readouts. For instance, HRP-NF@CNT-30Is is used to sensitively detect H2O2 in the range of 20 to 300 μM with an LOD of 2.26 μM. The catalytic activity of HRP-NF@CNT-30Is is suppressed in the presence of GSH, and then an obvious color change from blue to nearly colorless is observed. Using this strategy, GSH is also sensitively determined in the range of 20-200 μM with an LOD of 11.2 μM. We expect that HRP-NF@CNTs can be used as a promising and novel nanobiocatalyst for various biomedical and industrial applications in the near future.

MRI-guided dual-responsive anti-tumor nanostructures for synergistic chemo-photothermal therapy and chemodynamic therapy

Image-guided stimulus-responsive theranostics are beneficial for identifying malignant lesions and integrating multiple cell-killing mechanisms to enhance tumor cell clearance. Herein, an intelligent dual-responsive nanostructure (HSPMH-DOX) was developed for magnetic resonance imaging (MRI)-guided synergistic chemo-photothermal therapy (PTT) and chemodynamic therapy (CDT). The core-shell nanostructure was synthesized by layering polydopamine (PDA), manganese oxide (MnO₂), and hyaluronic acid (HA) onto drug-loaded hollow mesoporous silica nanoparticles (HS). The constructed nanoagent has both endogenous and external dual responses. The tumor microenvironment (pH/GSH) can trigger the degradation of gatekeeper (MnO₂ and PDA), resulting in the release of anti-tumor drugs, whereas external near-infrared light irradiation can accelerate the degradation process and generate local overheating, resulting in PTT. Notably, MnO₂ can not only consume intracellular GSH to enhance CDT but also release Mn²⁺ for precise localization of tumor tissues using MRI. Both in vitro and in vivo experiments showed that the prepared dual-response nanoagent satisfied biocompatibility, targeting, and the great efficiency of MRI-guided combined therapy. In animal models, combining chemo-PTT and CDT can eradicate tumors in less than two weeks. This work could pave the way for a wide range of stimulus-responsive synergistic theranostic applications, including MRI, chemo-photothermal therapy, and chemodynmic therapy. STATEMENT OF SIGNIFICANCE: Low bioavailability and severe side effects remain the major limitations of conventional cancer chemotherapy. Image-guided combination therapy can alleviate these problems and improve tumor-specific therapy. In the present study, the anticancer drug doxorubicin was encapsulated in a core-shell hollow mesoporous silica nanostructure (HSPMH-DOX), enabling MRI-guided targeted release under both endogenous and external dual stimuli. Moreover, the photothermal and nanoenzymatic effects of nanomedicine can cause local overheating in the tumor and amplify the intracellular CDT effect, accelerating tumor eradication. Systematic evaluations in vitro and in vivo confirmed that nanomedicine enables highly effective MRI-guided synergistic chemo-photothermal and chemodynamic therapy. This work offers a promising therapeutic strategy for precise anti-tumor applications.

Label-free ultra-sensitive colorimetric detection of hepatitis E virus based on oxidase-like activity of MnO2 nanosheets

Hepatitis E virus (HEV) is an evolving infectious entity that causes viral hepatitis infections worldwide. Current routine methods of identifying and diagnosing HEV are someway laborious and costly. Based on the biomimicking oxidase-like activity of MnO₂ nanosheets, we designed a label-free, highly sensitive colorimetric sensing technique for HEV detection. The prepared MnO₂ catalyst displays intrinsic biomimicking oxidase-like catalytic activity and efficiently oxidizes the 3,3',5,5'-tetramethylbenzidine (TMB) substrate from colorless to blue colored oxidized TMB (oxTMB) product which can be measured at 652 nm by UV-visible spectrum. When the HEV-DNA was added, DNA adsorbed easily on MnO₂ surface through physical adsorption and electrostatic interaction which hinders the oxidase-like catalytic activity of MnO₂. Upon the introduction of target, the HEV target DNA binds with its complementary ssDNA on the surface of MnO₂, the hybridized DNA releases from the surface of MnO₂, which leads to recovery of oxidase-like catalytic activity of MnO₂. This strategy was applied to construct a colorimetric technique for HEV detection. The approach works in the linear range of 1 fM-100 nM DNA concentration with the limit of detection (LOD) of 3.26 fM (S/N = 3) and quantitative limit (LOQ) of 36.08 fM. The TMB-MnO₂ platform was highly selective for HEV target DNA detection when compared with potential interferences. Result of serum sample analysis demonstrates that this sensing system can be used for clinical diagnostic applications.

Portable sensor based on magnetic separation and enzyme-mediated immune nanomaterials for point-of-care testing of Listeria monocytogenes in food

Listeria monocytogenes (L. monocytogenes), a typical foodborne pathogen, poses a serious threat to public health safety. This stimulates to develop a point-of-care testing (POCT) method to achieve rapid, sensitive detection of L. monocytogenes. In this study, polyethylene glycol (PEG) mediated ampicillin functionalized magnetic beads (Amp-PEG-MBs) was prepared successfully and it achieved high efficiency (>90%) and rapid (5 min) capture for L. monocytogenes at room temperature. The innovative combination of antibody (Ab), glucose oxidase (GOD) and graphene oxide (GO) prepared Ab@GO@GOD for the specific recognition of L. monocytogenes. Finally, Amp-PEG-MBs and Ab@GO@GOD were successfully assembled into Amp-PEG-MBs@L. monocytogenes-Ab@GO@GOD sandwich structure which could catalyze the glucose, and the final detection results were recorded by a blood glucose meter (BGM). Magnetic separation (MS) combined with enzyme-catalyzed sensor (MS-Ab@GO@GOD-BGM) was successfully established to achieve the detection of L. monocytogenes in artificially contaminated juice within 66 min with the limit of detection was 10¹ CFU/mL. This sensor has potential for other pathogens detection by modifying specific antibodies.

NIR-II-responsive AuNRs@SiO2-RB@MnO2 nanotheranostic for multimodal imaging-guided CDT/PTT synergistic cancer therapy

Specific tumor-responsive capabilities and efficient synergistic therapeutic performance are the keys to effective tumor treatment. Herein, AuNRs@SiO₂-RB@MnO₂ was developed as a new type of tumor-responsive nanotheranostic for multimodal imaging and synergistic chemodynamic/photothermal therapy. In AuNRs@SiO₂-RB@MnO₂, the SiO₂ layer wraps the AuNRs, providing light absorption in the second near-infrared (NIR-II) region. The SiO₂ layer also adsorbs the MnO₂ nanosheets, which have Fenton-like activity, resulting in a fluorescent sensing platform based on the fluorescence quenching properties of MnO₂ for rhodamine B dye. The fluorescence can be recovered by the consumption of MnO₂ by glutathione, which simultaneously produces Mn²⁺ in the tumor region. The recovery of fluorescence reflects the consumption of glutathione and the increase in Mn²⁺, which produces hydroxyl radicals via Fenton-like reaction in the tumor microenvironment to realize chemodynamic therapy. Meanwhile, the AuNRs are a good photothermal reagent that can effectively absorb NIR-II light and convert it into heat energy to kill tumor cells via photothermal therapy. The NIR-II absorption performance of the AuNRs provides good photoacoustic imaging and deep photothermal performance, which is favorable for efficient NIR-II photoacoustic imaging-guided photothermal therapy. As a result, the AuNRs@SiO₂-RB@MnO₂ nanotheranostic exhibits outstanding imaging and synergistic chemodynamic/photothermal therapeutic performance for tumor imaging and treatment.

Imaging Intracellular Drug/siRNA Co-Delivery by Self-Assembly Cross-Linked Polyethylenimine with Fluorescent Core-Shell Silica Nanoparticles

Multifunctional theranostic nanomaterial represents one type of emerging agent with the potential to offer both sensitive diagnosis and effective therapy. Herein, we report a novel drug/siRNA co-delivery nanocarrier, which is based on fluorescent mesoporous core-shell silica nanoparticles coated by cross-linked polyethylenimine. The fluorescent mesoporous core-shell silica nanoparticles can provide numerous pores for drug loading and negative charged surface to assemble cross-linked polyethylenimine via electrostatic interaction. Disulfide cross-linked polyethylenimine can be absorbed on the surface of silica nanoparticles which provide the feasibility to bind with negatively charged siRNA and release drug "on-demand". In addition, the hybrid nanoparticles can be easily internalized into cells to realize drug/siRNA co-delivery and therapeutic effect imaging. This work would stimulate interest in the use of self-assembled cross-linked polyethylenimine with fluorescent mesoporous core-shell silica nanoparticles to construct multifunctional nanocomposites for tumor therapy.

Mesoporous Silica Nanoparticles in Chemical Detection: From Small Species to Large Bio-Molecules

A recompilation of applications of mesoporous silica nanoparticles in sensing from the last five years is presented. Its high potential, especially as hybrid materials combined with organic or bio-molecules, is shown. Adding to the multiplying effect of loading high amounts of the transducer into the pores, the selectivity attained by the interaction of the analyte with the layer decorating the material is described. Examples of the different methodologies are presented.

SERS Sensors Based on Aptamer-Gated Mesoporous Silica Nanoparticles for Quantitative Detection of Staphylococcus aureus with Signal Molecular Release

This work describes a simple and novel biosensor for the quantitative determination of Staphylococcus aureus (S. aureus) based on target-induced release of signal molecules from aptamer-gated aminated mesoporous silica nanoparticles (MSNs) coupled with surface-enhanced Raman scattering (SERS) technology. MSNs were synthesized and then modified with amino groups by (3-aminopropyl) triethoxysilane to make them positively charged. Next, signal molecules (4-aminothiophenol, 4-ATP) were loaded into the pores of MSNs. Then, negatively charged aptamers of S. aureus were assembled on the surface of MSNs through electrostatic interactions. Upon the addition of S. aureus, the assembled aptamers were specifically bound to the bacteria. Consequently, the "gates" were opened, resulting in the release of 4-ATP from the pores of MSNs. The released molecules were measured by a Raman spectrometer, and the intensity of 4-ATP at 1071 cm^-1 was linearly related to the S. aureus concentration. A silver nanoflower silica core-shell structure (Ag NFs@SiO₂) was prepared and it served as a SERS substrate. Under optimized experimental conditions, a good linear relationship (y = 2107.93 + 1536.30x, R² = 0.9956) in the range from 4.7 × 10 to 4.7 × 10⁸ cfu/mL was observed with a limit of detection of 17 cfu/mL. The method was successfully applied for the analysis of S. aureus in fish samples and the recovery rate was 91.3-109%.

Biosensors Coupled with Signal Amplification Technology for the Detection of Pathogenic Bacteria: A Review

Foodborne disease caused by foodborne pathogens is a very important issue in food safety. Therefore, the rapid screening and sensitive detection of foodborne pathogens is of great significance for ensuring food safety. At present, many research works have reported the application of biosensors and signal amplification technologies to achieve the rapid and sensitive detection of pathogenic bacteria. Thus, this review summarized the use of biosensors coupled with signal amplification technology for the detection of pathogenic bacteria, including (1) the development, concept, and principle of biosensors; (2) types of biosensors, such as electrochemical biosensors, optical biosensors, microfluidic biosensors, and so on; and (3) different kinds of signal amplification technologies applied in biosensors, such as enzyme catalysis, nucleic acid chain reaction, biotin-streptavidin, click chemistry, cascade reaction, nanomaterials, and so on. In addition, the challenges and future trends for pathogenic bacteria based on biosensor and signal amplification technology were also discussed and summarized.

A turn-on fluorescence strategy for cellular glutathione determination based on the aggregation-induced emission enhancement of self-assembled copper nanoclusters

As a class of ideal fluorescent nanomaterials, self-assembled copper nanoclusters (CuNCs) have attracted increasing interest. Unfortunately, most of these CuNCs only possessed bright luminescence in acidic solution, which limited their practical applications in a physiological environment. Retaining the strong fluorescence of these CuNCs in neutral or alkaline solution is still a challenging task. In this strategy, self-assembled CuNCs were prepared by using 4-methylthiophenol as the protecting ligand. The self-assembled CuNCs display stable and bright luminescence with excitation/emission maxima at 330/605 nm even in neutral and alkaline environments. Interestingly, with the addition of glutathione (GSH), the fluorescence intensity of CuNCs is enhanced strongly through the GSH-controlled aggregation-induced emission enhancement of self-assembled CuNCs. The turn-on fluorescence strategy can determine the GSH concentration in the range from 1 to 100 μM with a limit of detection of 300 nM. In addition, the method is employed for the determination of GSH levels in cells. Therefore, the turn-on fluorescence strategy is reliable, sensitive and suitable for the determination of cellular GSH levels.

Fluorescent and colorimetric determination of glutathione based on the inner filter effect between silica nanoparticle-gold nanocluster nanocomposites and oxidized 3,3',5,5'-tetramethylbenzidine

Determination of glutathione (GSH) is closely related to the clinical diagnosis of many diseases. Thus, a fluorescent and colorimetric dual-readout strategy for the sensitive determination of glutathione was proposed. The mesoporous silica nanoparticle-gold nanocluster (MSN-AuNC) nanocomposites with significantly enhanced emission and effectively improved photostability characteristics were used as fluorescent probes. Based on the inner filter effect (IFE), the fluorescence of MSN-AuNCs at 570 nm can be effectively quenched by oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) with absorption in the wavelength ranges of 330-470 nm and 500-750 nm. However, the addition of GSH could cause the reduction of blue oxTMB to colorless TMB, resulting in the inhibition of IFE and the recovery of the fluorescence of MSN-AuNCs. Therefore, using oxTMB as both quencher and color indicator, a dual-readout oxTMB/MSN-AuNC sensing system for the sensitive determination of GSH was constructed. As signal amplification is caused by the fluorescence enhancement of MSN-AuNCs, the detection limits as low as 0.12 μM and 0.34 μM can be obtained for fluorescent and colorimetric assay, respectively. This method may not only offer a new idea for the sensitive and effective determination of GSH, but also broaden the applications of AuNCs in fluorescent and colorimetric dual-readout bioanalysis.

Portable detection of Staphylococcus aureus using personal glucose meter based on hybridization chain reaction strategy

Staphylococcus aureus is one of the most important food-borne bacterial pathogens and causes numerous illnesses. In this work, we report a sensitive and highly selective magnetic-aptamer biosensor based on a personal glucose meter (PGM) platform for the detection of Staphylococcus aureus. The aptamer for Staphylococcus aureus was immobilized on the magnetic bead by hybridization with the capture probe P. In the presence of Staphylococcus aureus, the aptamer was dissociated from the magnetic bead. Then the capture probe was exposed and could be hybridized with a biotinylated probe to trigger the DNA hybridization chain reaction (HCR), thus achieving the signal amplification. The concentration of streptavidin-labeled invertase can be read by PGM, thus can lead to the portable quantitative detection of Staphylococcus aureus. After optimization of various conditions, 5 μM probe P, the MB-P reaction time for 36 h, the competition time for 60 min, 0.5 μM H1 & H2, 0.5 M sucrose and the sucrose invertase catalytic reaction time for 50 min was chosen to achieve the better sensor performance. Under the optimal conditions, the fabricated sensor offers high sensitivity with the limit of detection about 2 CFU/mL. This sensitive PGM based sensor could successfully evaluate the Staphylococcus aureus concentration in real food samples, and the results are consistent with those obtained by using plate counting methods. Moreover, the PGM sensor can greatly reduce the required time compared to the plate counting methods. The fabricated sensor supplies an ideal solution for rapid portable detection of bacterial pathogens and holds its potential use in the quality control for agriculture and food enterprises, entry-exit inspection and quality testing for food.

Ratiometric fluorescence sensing of glutathione by using the oxidase-mimicking activity of MnO2 nanosheet

In this work, a facile ratiometric fluorescence sensor for GSH measurement was designed based on MnO₂ nanosheet (NS), carbon dots (CDs), as well as a simple substrate o-phenylenediamine (OPD). Herein, MnO₂ NS played triple essential roles in the sensing system. First, it could be reduced by GSH through a special reaction, and therefore served as GSH recognizer. Second, it played as a fluorescence nanoquencher to strongly quench the fluorescence of CDs. Third, it could directly oxidize OPD to yield a luminescent product 2, 3-diaminophenazine (DAP) via the intrinsic oxidase-like activity. It revealed that MnO₂ NS could be reduced to Mn²⁺ in the presence of GSH. Thus its oxidase-like activity and fluorescence quenching abilities were inhibited, which then restricted the generation of DAP and recovered the fluorescence of CDs. Based on this phenomenon, a novel ratiometric fluorescence sensor for GSH determination was fabricated by measuring the ratio of fluorescent intensity of DAP to that of CDs. Besides, the constructed ratiometric fluorescent sensor, which could be facilely operated with single-wavelength excitation, exhibited high sensitivity and selectivity with a wider linear range and a lower detection limit.

Translating in vitro diagnostics from centralized laboratories to point-of-care locations using commercially-available handheld meters

There is a growing demand for high-performance point-of-care (POC) diagnostic technologies where in vitro diagnostics (IVD) is fundamental for prevention, identification, and treatment of many diseases. Over the past decade, a shift of IVDs from the centralized laboratories to POC settings is emerging. In this review, we summarize recent progress in translating IVDs from centralized labs to POC settings using commercially available handheld meters. After introducing typical workflows for IVDs and highlight innovative technologies in this area, we discuss advantages of using commercially available handheld meters for translating IVDs from centralized labs to POC settings. We then provide comprehensive coverage of different signal transduction strategies to repurpose the commercially-available handheld meters, including personal glucose meter, pH meter, thermometer and pressure meter, for detecting a wide range of targets by integrating biochemical assays with the meters for POC testing. Finally, we identify remaining challenges and offer future outlook in this area.

2D MnO2 nanosheets generated signal transduction with 0D carbon quantum dots: synthesis strategy, dual-mode behavior and glucose detection

A natural resource such as peony flower has been employed for the first time as a new carbon precursor to prepare green-emitting carbon nanodots (CDs). The emission peak is situated at 523 nm and the excitation wavelength can be extended to the visible light range (452 nm). Due to the formation of CD-MnO₂ nanocomposites, the emission intensity of CDs is sharply reduced as a consequence of Förster resonance energy transfer (FRET). Moreover, glucose can be recognized due to the enzymatic conversion of glucose by glucose oxidase to generate H₂O₂. The MnO₂ nanosheets are reduced to form Mn(ii) ions, and the fluorescence of CDs can be recovered. The fluorescence intensity has been improved linearly based on the increasing concentration of glucose (0.5-250 μM) with a detection limit as low as 0.18 μM. This strategy gives a new selection of eco-friendly precursors in carbon nanomaterials and such a consecutive recognition process provides valuable insights for bio-analysis.

Manganese dioxide nanosheets: from preparation to biomedical applications

Advancements in nanotechnology and molecular biology have promoted the development of a diverse range of models to intervene in various disorders (from diagnosis to treatment and even theranostics). Manganese dioxide nanosheets (MnO₂ NSs), a typical two-dimensional (2D) transition metal oxide of nanomaterial that possesses unique structure and distinct properties have been employed in multiple disciplines in recent decades, especially in the field of biomedicine, including biocatalysis, fluorescence sensing, magnetic resonance imaging and cargo-loading functionality. A brief overview of the different synthetic methodologies for MnO₂ NSs and their state-of-the-art biomedical applications is presented below, as well as the challenges and future perspectives of MnO₂ NSs.

Aptamer based determination of the cancer biomarker HER2 by using phosphate-functionalized MnO2 nanosheets as the electrochemical probe

The authors report a sensitive electrochemical aptamer-based assay for the cancer biomarker human epidermal growth factor receptor-2 (HER2). It is based on the use of MnO₂ nanosheets that were functionalized with phosphate and a HER2 binding aptamer and serve as the electrochemical probe. The assay follows a sandwich protocol. A peptide that can specifically recognize HER2 was immobilized on a gold electrode for the capture of HER2. Then, the functionalized MnO₂ nanosheets were linked to the electrode via the binding between HER2 and HER2 aptamer on the MnO₂ nanosheets. The reaction of phosphate and aptamer on the MnO₂ nanosheets with molybdate leads to the formation of redox-active molybdophosphate. This results in dual signal amplification. The generated electrochemical current was measured at 0.22 V (vs. Ag/AgCl). The assay allows HER2 to be determined in the 0.1 to 500 pg·mL^-1 concentration range, and the detection limit is as low as 0.05 pg·mL^-1. The assay was successfully applied for the detection of HER2 in spiked human serum samples. Graphical abstract Electrochemical detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing phosphate ions and aptamer functionalized MnO₂ nanosheet as probe.

Human serum albumin templated MnO2 nanosheets are oxidase mimics for colorimetric determination of hydrogen peroxide and for enzymatic determination of glucose

This paper reports on a colorimetric assay for H₂O₂ and glucose. It is based on the use of human serum albumin-templated MnO₂ nanosheets that possess oxidase-like activity. They are capable of oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with oxygen to give a blue product (oxTMB) with an absorbance maximum at 652 nm. When H₂O₂ is introduced, the MnO₂ nanosheets are reduced to Mn(II) ions, and this inhibits the formation of oxTMB. Based on these findings, a colorimetric assay was established for H₂O₂ that has a 0.56 μM detection limit. If glucose is oxidized by glucose oxidase under formation of H₂O₂, the nanosheets can be used to quantify H₂O₂ and thereby to sense glucose. Response is linear in the 0.5 μM to 50 μM glucose concentration range, and the detection limit is 0.32 μM. The method was applied to the determination of glucose in spiked serum samples and gave satisficatory results. Graphical abstract Human serum albumin (HSA) is used as a template for the synthesis of MnO₂ nanosheet. These possess oxidase mimicking activity. H₂O₂ can reduce the nanosheets. The effect is exploited in colorimetric assays for H₂O₂ and glucose using tetramethylbenzidine (TMB) as a chromogenic substrate.

New insights into the structure-performance relationships of mesoporous materials in analytical science

Mesoporous materials are ideal carriers for guest molecules and they have been widely used in analytical science. The unique mesoporous structure provides special properties including large specific surface area, tunable pore size, and excellent pore connectivity. The structural properties of mesoporous materials have been largely made use of to improve the performance of analytical methods. For instance, the large specific surface area of mesoporous materials can provide abundant active sites and increase the probability of contact between analytes and active sites to produce stronger signals, thus leading to the improvement of detection sensitivity. The connections between analytical performances and the structural properties of mesoporous materials have not been discussed previously. Understanding the "structure-performance relationship" is highly important for the development of analytical methods with excellent performance based on mesoporous materials. In this review, we discuss the structural properties of mesoporous materials that can be optimized to improve the analytical performance. The discussion is divided into five sections according to the analytical performances: (i) selectivity-related structural properties, (ii) sensitivity-related structural properties, (iii) response time-related structural properties, (iv) stability-related structural properties, and (v) recovery time-related structural properties.

Liposome-coated mesoporous silica nanoparticles loaded with L-cysteine for photoelectrochemical immunoassay of aflatoxin B1

The authors describe a photoelectrochemical (PEC) immunoassay for determination of aflatoxin B1 (AFB1) in foodstuff. The competitive immunoreaction is carried out on a microplate coated with a capture antibody against AFB1 using AFB1-bovine serum albumin (BSA)-liposome-coated mesoporous silica nanoparticles (MSN) loaded with L-cysteine as a support. The photocurrent is produced by a photoactive material consisting of cerium-doped Bi2MoO6. Initially, L-cysteine acting as the electron donor is gated in the pores by interaction between mesoporous silica and liposome. Thereafter, AFB1-BSA conjugates are covalently bound to the liposomes. Upon introduction of the analyte (AFB1), the labeled AFB1-BSA complex competes with the analyte for the antibody deposited on the microplate. Accompanying with the immunocomplex, the liposomes on the MSNs are lysed upon addition of Triton X-100. This results in the opening of the pores and in a release of L-cysteine. Free cysteine then induces the electron-hole scavenger of the photoactive nanosheets to increase the photocurrent. The photocurrent (relative to background signal) increases with increasing AFB1 concentration. Under optimum conditions, the photoactive nanosheets display good photoelectrochemical responses, and allow the detection of AFB1 at a concentration as low as 0.1 pg·mL-1 within a linear response in the 0.3 pg·mL-1 to 10 ng·mL-1 concentration range. Accuracy was evaluated by analyzing naturally contaminated and spiked peanut samples by using a commercial AFB1 ELISA kit as the reference, and well-matching results were obtained. Graphical abstract Schematic presentation of a photoelectrochemical immunoassay for AFB1. It is based on the use of Ce-doped Bi2MoO6 nanosheets and of liposome-coated mesoporous silica nanoparticles loaded with L-cysteine.

Sensitive fluorescence detection of heparin based on self-assembly of mesoporous silica nanoparticle–gold nanoclusters with emission enhancement characteristics

Sensitive fluorescence detection of heparin based on self-assembly of mesoporous silica nanoparticle–gold nanoclusters with emission enhancement characteristics was reported.

A facile fluorescence assay for rapid and sensitive detection of uric acid based on carbon dots and MnO2nanosheets

A sensitive turn-on fluorescence method for uric acid detection is proposed based on FRET between carbon dots and MnO₂nanosheets.

A MnO2nanosheets–o-phenylenediamine oxidative system for the sensitive fluorescence determination of alkaline phosphatase activity

A MnO₂nanosheets–o-phenylenediamine (OPDA) oxidative system was developed for detecting ALP activity selectively, sensitively and conveniently.