Highly sensitive GQDs-MnO2 based assay with turn-on fluorescence for monitoring cerebrospinal acetylcholinesterase fluctuation: A biomarker for organophosphorus pesticides poisoning and management

Poria cocos-derived carbon dots for parallel detection of Cr6+/Fe3+ in complex environments with superior sensitivity

Multifunctional sensor capable of parallel sensing is of great importance thanks to their wide applications and great practicality. In this report, Poria cocos-derived carbon dots (CDs) were adopted for the development of multifunctional sensor for the parallel detection of Cr6+ and Fe3+ with superior sensitivity and applicability. Specifically, extremely low limit of detection (LOD) of 1.07 × 10-3 nM and 1.98 × 10-3 nM were achieved for Cr6+ and Fe3+, respectively. Systematic mechanism explorations revealed that the highly sensitive detection of Cr6+ was attributed to an efficient inner filter effect (IFE), while the sensing of Fe3+ was realized due to a strong static quenching process. Furthermore, the assay was found to be extremely versatile, achieving the reliable detection of Cr6+ and Fe3+ in multiple natural water environments and even biological environment. Utilizing the different reactions of Cr6+ and Fe3+ towards masking reagents, a logic gate that could effectively eliminate the mutual interference of Cr6+ and Fe3+ was successfully designed.

Upconversion-based hydrogel kit with Python-assisted analysis platform for sample-to-result detection of organophosphorus pesticide

On-site quantitative analysis of pesticide residues is crucial for monitoring environmental quality and ensuring food safety. Herein, we have developed a reliable hydrogel portable kit using NaYbF4@NaYF4: Yb, Tm upconversion nanoparticles (UCNPs) combined with MnO2 nanoflakes. This portable kit is integrated with a smartphone reader and Python-assisted analysis platform to enable sample-to-result analysis for chlorpyrifos. The novel UCNPs maximizes energy donation to MnO2 acceptor by employing 100 % of activator Yb3+ in the nucleus for NIR excitation energy collection and confining emitter Tm3+ to the surface layer to shorten energy transfer distance. Under NIR excitation, efficient quenching of upconversion blue-violet emission by MnO2 nanoflakes occurs, and the quenched emission is recovered with acetylcholinesterase-mediated reactions. This process allows for the determination of chlorpyrifos by inhibiting enzymatic activity. The UCNPs/MnO2 were embedded to fabricate a hydrogel portable kit, the blue-violet emission images captured by smartphone were converted into corresponding gray values by Python-assisted superiority chart algorithm which achieves a real-time rapid quantitative analysis of chlorpyrifos with a detection limit of 0.17 ng mL-1. At the same time, pseudo-color images were also added by Python in "one run" to distinguish images clearly. This sensor detection with Python-assisted analysis platform provides a new perspective on pesticide monitoring and broadens the application prospects in bioanalysis.

Superior oxidase-mimetic activity of FeCo-NC dual-atom nanozyme for smartphone-based visually colorimetric assay of organophosphorus pesticides

A colorimetric analysis platform has been successfully developed based on FeCo-NC dual-atom nanozyme (FeCo-NC DAzyme) for the detection of organophosphorus pesticides (OPPs). The FeCo-NC DAzyme exhibited exceptional oxidase-like activity (OXD), enabling the catalysis of colorless TMB to form blue oxidized TMB (oxTMB) without the need for H2O2 involvement. By combining acid phosphatase (ACP) hydrolase with FeCo-NC DAzyme, a "FeCo-NC DAzyme + TMB + ACP + SAP" colorimetric system was constructed, which facilitated the rapid detection of malathion. The chromogenic system was applied to detect malathion using a smartphone-based app and an auxiliary imaging interferogram device for colorimetric measurements, which have a linear range of 0.05-4.0 µM and a limit of detection (LOD) as low as 15 nM in real samples, comparable to UV-Vis and HPLC-DAD detection methods. Overall, these findings present a novel approach for convenient, rapid, and on-site monitoring of OPPs.

Ultrasensitive Fluorescence Platform Based on AgNPs In Situ-Incorporated Zr-MOFs for the Detection of Organophosphorus Pesticides

Organophosphorus pesticides (OPPs) are extensively used in agricultural production, and the contamination caused by their residues has raised significant concerns regarding potential threats to human health. Herein, a novel fluorescence nanoprobe based on an enzyme-mediated silver nanoparticle-modified metal organic framework (AgNPs@PCN-224) was successfully prepared for the rapid detection of OPPs. Initially, AgNPs@PCN-224 were synthesized by reducing silver nitrate (AgNO3) using sodium borohydride (NaBH4) embedded into luminescent PCN-224. This triggered the inner filter effect, leading to fluorescence quenching. Meanwhile, under the catalysis of acetylcholinesterase (AChE) and choline oxidase (CHO), acetylcholine (ATCh) was decomposed to hydrogen peroxide (H2O2), which could destroy AgNPs to form Ag+ released from PCN-224 for fluorescence recovery. Instead, fenitrothion, an OPP, inhibited AChE activity, allowing the quenched fluorescence to be reactivated. Under the current optimum conditions, the fluorescence intensity had a good correlation (Y = -728.5370X + 2178.4248, R2 = 0.9869) over a dynamic range of fenitrothion concentrations from 0.1 to 500 ng/mL, with an LOD of 0.037 ng/mL. In addition, the anti-interference ability and robustness of the proposed sensor was verified for the monitoring of fenitrothion in tea with recoveries of 87.67-103.72% and the relative standard deviations (RSD) < 5.43%, indicating that the system has excellent prospects for OPP determination in practical applications. Furthermore, this work provides a universal platform for screening other enzyme inhibitors to detect OPPs.

Biochemical responses as early and reliable biomarkers of organophosphate and carbamate pesticides intoxication: A systematic literature review

Inhibition of cholinesterase (ChE) activity has been long considered as the main diagnostic method of organophosphate (OP) and carbamate pesticides poisoning; however, it has been shown that ChE activity may also be altered due to exposure to other non-organophosphorus toxicants and variety of different medical conditions. Hence, to avoid misdiagnosis, we aimed to systematically review available documents to look for additional biomarkers of OP and carbamate poisoning. The electronic databases in addition to Google scholar were searched for eligible articles on March 2022 using "organophosphate," "carbamate," and "biomarker" including all their similar terms. After collecting the relevant documents, the data were extracted and described qualitatively. In total, data of 66 articles from 51 human and 15 animal studies were extracted. Findings demonstrated that enzymes such as β-glucuronidase, neuropathy target esterase, amylase, and lipase, in addition to hematological indicators such as CBC, CRP, lactate dehydrogenase, and CPK have high sensitivity and accuracy in the diagnosis of OP poisoning. Findings suggest that using various markers for diagnosis of OP intoxication is helpful for appropriate management, and early identifying the patients at risk of death. The suggested biomarkers also help to avoid misdiagnosis of OP poisoning with other similar conditions.

Graphitic-phase C3N4 nanosheets combined with MnO2 nanosheets for sensitive fluorescence quenching detection of organophosphorus pesticides

In this study, we have developed a sensitive approach to measure organophosphorus pesticides (OPs) using graphitic-phase C₃N₄ nanosheets (g-C₃N₄) combined with a nanomaterial-based quencher, MnO₂ nanosheets (MnO₂ NS). Since MnO₂ NS can quench the fluorescence of g-C₃N₄ via the inner-filter effect (IFE), enzymatic hydrolysate (thiocholine, TCh) can efficiently trigger the decomposition of MnO₂ nanosheets in the presence of acetylcholinesterase (AChE) and acetylthiocholine (ATCh), resulting in the fluorescence recovery of g-C₃N₄. OPs, as inhibitors to AChE activity, can prevent the generation of TCh and decomposition of MnO₂ nanosheets while exhibiting fluorescence quenching. Therefore, the AChE-ATCh-MnO₂-g-C₃N₄ system can be utilized to quantitatively detect OPs based on g-C₃N₄ fluorescence. Under optimal conditions, the linear ranges for the determination of parathion-methyl (PM) and 2,2-dichlorovinyl dimethyl phosphate (DDVP) were found to be 0.1-2.1 ng/mL and 0.5-16 ng/mL, respectively, with limits of detection of 0.069 ng/mL and 0.20 ng/mL, respectively. The advantages of this assay are user-friendliness, ease of use, and cost effectiveness compared to other more sophisticated analytical instruments.

Discovery of Novel Acetylcholinesterase Inhibitors by Virtual Screening, In Vitro Screening, and Molecular Dynamics Simulations

Alzheimer's disease is the most common neurodegenerative disease and currently poses a significant socioeconomic problem. This study describes the uses of computer-aided drug discovery techniques to identify novel inhibitors of acetylcholinesterase, a target for Alzheimer's disease. High-throughput virtual screening was employed to predict potential inhibitors of acetylcholinesterase. Validation of enrichment was performed with the DUD-E data set, showing that an ensemble of binding pocket conformations is critical when a diverse set of ligands are being screened. A total of 720 compounds were submitted for in vitro screening, which led to 25 hits being identified with IC₅₀ values of less than 50 μM. The majority of these hits belonged to two scaffolds: 1-ethyl-3-methoxy-3-methylpyrrolidine and 1H-pyrrolo[3,2-c]pyridin-6-amine both of which are noted to be promising compounds for further optimization. As various possible binding poses were suggested from molecular docking, molecular dynamics simulations were employed to validate the poses. In the case of the most active compounds identified, a critical, stable water bridge formed deep within the binding pocket was identified potentially explaining in part the lack of activity for subsets of compounds that are not able to form this water bridge.

Sensitivity Dependence on the Crystal Forms of a Fluorescence Quencher for Silicon Quantum Dots and Its Use in Acetylcholinesterase Assay

Acetylcholinesterase (AChE) plays crucial roles in the nervous system, and thus the reliable assay of its activity is of great significance for the diagnosis of nervous diseases. In this work, we report a fluorescent sensing platform with silicon quantum dots (Si-QDs) as a fluorescence oscillator and nano iron oxyhydroxide (α-, β-, and γ-FeOOH) as a quencher for the assay of AChE. FeOOH with α-, β-, and γ-crystal forms quenches the fluorescence of Si-QDs at λ_ex/λ_em = 350/438 nm, which is retrieved in the presence of AChE and its substrate acetylthiocholine (ATCh) to provide an off-on strategy with a high signal/noise ratio. It is interesting that the sensitivity of AChE sensing is closely related to the crystal forms of FeOOH, with the highest sensitivity by adopting α-FeOOH as the quencher. A linear calibration is achieved within 0.02-1.4 U/L along with a limit of detection of 0.016 U/L. The sensing strategy was demonstrated by the AChE assay in human blood, plasma, and hemocytes.

A Lab-in-a-Syringe Device Integrated with a Smartphone Platform: Colorimetric and Fluorescent Dual-Mode Signals for On-Site Detection of Organophosphorus Pesticides

Herein, a portable lab-in-a-syringe device integrated with a smartphone sensing platform was designed for rapid, visual quantitative determination of organophosphorus pesticides (OPs) via colorimetric and fluorescent signals. The device was chiefly made up of a conjugate pad labeled with cetyltrimethylammonium bromide-coated gold nanoparticles (CTAB-Au NPs) and a sensing pad modified by ratiometric probes (red-emission quantum dots@SiO₂ nanoparticles@green-emission quantum dots, rQDs@SiO₂@gQDs probe), which was assembled through a disposable syringe and reusable plastic filter. In the detection system, thiocholine (Tch), the hydrolysis product of thioacetylcholine (ATch) by acetylcholinesterase (AchE), could trigger the aggregation of CTAB-Au NPs, resulting in a significant color change from red to purple. Then, CTAB-Au NPs flowed vertically upward and bound to the rQDs@SiO₂@gQDs probe on the sensing pad, reducing the fluorescence resonance energy transfer effect between CTAB-Au NPs and gQDs. Meanwhile, rQDs embedded in SiO₂ NPs remained stable as internal reference fluorescence, achieving a color transition from red to green. Thus, based on the inhibition of AChE activity by OPs, a colorimetric and fluorescent dual-mode platform was constructed for on-site detection of OPs. Using glyphosate as a model, with the support of a color recognizer application (APP) on a smartphone, the ratio of red and green channel values could be utilized for accurate OP quantitative analysis ranging from 0 to 10 μM with a detection limit of 2.81 nM (recoveries, 90.8-122.4%; CV, 1.2-3.4%). Overall, the portable lab-in-a-syringe device based on a smartphone sensing platform integrated sample monitoring and result analysis in the field, implying great potential for on-site detection of OPs.

Red-to-blue paper-based colorimetric sensor integrated with smartphone for point-of-use analysis of cerebral AChE upon Cd2+ exposure

Herein, combined with a pervasive smartphone installed with a color recognition app, dual-responsive CDs@Eu/GMP ICPs were designed as a red-to-blue paper-based colorimetric sensor for the point-of-use analysis of cerebral acetylcholinesterase (AChE) upon Cd2+ exposure. Blue-emitting CDs with multi-functional groups as guests were encapsulated into the network of Eu/GMP ICPs to obtain CDs@Eu/GMP ICPs with the sensitized red fluorescence of Eu3+. With the presence of thiocholine (TCh), derived from acetylthiocholine (ATCh) hydrolyzed by AChE, the coordination environment of the CDs@Eu/GMP ICPs was interrupted, leading to the collapse of the CDs@Eu/GMP ICP network and the corresponding release of guest CDs into the surrounding environment. Consequently, the sensitized red fluorescence of Eu3+ decreased and the blue fluorescence of the CDs increased. This obvious red-to-blue fluorescent color changes of CDs@Eu/GMP ICPs on test paper could then be integrated with the smartphone for point-of-use analysis of cerebral AChE upon Cd2+ exposure, which not only offers a new analytical platform for a better understanding of the environmental risk of Alzheimer's Dementia (AD), but also holds great potential in the early diagnosis of AD even at the asymptomatic stage with the decrease in CSF AChE as an early biomarker.

Cu2+-Regulated reversible coordination interaction of GQD@Tb/GMP ICP nanoparticles: towards directly monitoring cerebrospinal acetylcholinesterase as a biomarker for cholinic brain dysfunction

This work demonstrates a new strategy for sensing cerebrospinal acetylcholinesterase (AChE) as a cholinergic biomarker for brain dysfunction based on graphene quantum dot (GQD)-functionalized lanthanide infinite coordination polymer (Ln-ICP) nanoparticles. The ICPs used in this work were comprised of two components, i.e. a supramolecular Ln-ICP host formed by the coordination between the GMP ligand and central metal ion Tb3+, and guest GQDs with abundant functional groups, which were utilized as antenna ligands to further sensitize the fluorescence of Tb/GMP. Upon excitation at 300 nm, the obtained GQD@Tb/GMP ICP nanoparticles exhibited enhanced green fluorescence from Tb/GMP. With the addition of Cu2+, the competitive coordination between Cu2+ and GQDs weakened the antenna effect, leading to a decrease in the fluorescence of GQD@Tb/GMP ICPs. However, in the presence of thiocholine (TCh), a thiol-containing compound hydrolyzed from acetylthiocholine (ATCh) by AChE, a stronger coordination interaction between Cu2+ and TCh occurred, resulting in the restoration of the fluorescence of GQD@Tb/GMP ICPs. Using the method established herein, the cerebrospinal AChE fluctuation of rats with acute organophosphorus pesticide (OP) poisoning or chronic Alzheimer's disease (AD) could be monitored. This study essentially provides a novel approach to realize the direct monitoring of a biomarker for brain dysfunction by regulating the competitive coordination interaction reversibly, which is critical in the early diagnosis and therapy of brain diseases.

Stimulus Response of GQD-Sensitized Tb/GMP ICP Nanoparticles with Dual-Responsive Ratiometric Fluorescence: Toward Point-of-Use Analysis of Acetylcholinesterase and Organophosphorus Pesticide Poisoning with Acetylcholinesterase as a Biomarker

In this study, by rationally designing the stimulus response of graphene quantum dot (GQD)-sensitized terbium/guanine monophosphate (Tb/GMP) infinite coordination polymer (ICP) nanoparticles, we have constructed a smartphone-based colorimetric assay with ratiometric fluorescence, which could be applied for the detection of acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) directly. First, GQDs with abundant functional groups were chosen as the guest, which not only could be used as one of the signal readouts but also served as the antenna ligand to further sensitize the fluorescence of the host Tb/GMP. Upon being excited at 330 nm, the green fluorescence of the Tb/GMP host is highly enhanced, while the blue fluorescence of GQDs is suppressed due to the confinement of the ICP host. With the presence of thiocholine (TCh), an enzymatic product hydrolyzed from acetylthiocholine (ATCh) by AChE, the competitive coordination of Tb³⁺ between GMP and TCh results in the collapse of the ICP network and thereby the release of GQDs into the solution; thus, the fluorescence of Tb/GMP turns off and the fluorescence of GQDs turns on. The dual-responsive ratiometric fluorescent intensity change leads to the corresponding green-to-blue fluorescent color change obviously, which constitutes a novel mechanism for the colorimetric analysis of AChE. Moreover, when OPs are subsequently introduced, the activity of AChE is blocked, thus preventing the stimulus response of GQD@Tb/GMP ICP nanoparticles, leading to the fluorescent color change from greenish-blue to green, which could also be employed for OP detection. Benefitting from the high sensitivity, good reliability, and the obvious color changes, the method demonstrated here is a promising candidate to realize smartphone-based point-of-use applications, which is of great importance for timely clinical diagnosis and treatment of OPs related to health issues with AChE as an exposure biomarker in less industrialized countries, in remote settings, or even in home care services.

Biomedical application of manganese dioxide nanomaterials

Manganese dioxide nanomaterial is a new type of inorganic nanomaterial offering numerous advantages: simple preparation, low cost, and environmental friendliness. This review summarizes the traditional and novel synthetic methods for manganese dioxide nanomaterials and mainly discusses their potential in biomedical applications. Manganese dioxide nanomaterials are mainly used as drug carriers in tumor therapy. In recent years, the construction of multifunctional nano-platforms using manganese dioxide has gradually improved. The main mechanism is that manganese dioxide nanomaterials can combine with reactive oxygen species in the tumor microenvironment to alleviate tumor hypoxia. Manganese dioxide has also been used to quench fluorescent carbon dots in fluorescent probes. Based on the oxidation ability and catalytic activity of MnO₂, MnO₂ nanosheets are widely used to build biosensors. New research shows that manganese dioxide nanomaterials also have great potential in gene therapy and nuclear magnetic imaging.

Carbon dots sensitized lanthanide infinite coordination polymer nanoparticles: Towards ratiometric fluorescent sensing of cerebrospinal Aβ monomer as a biomarker for Alzheimer's disease

Herein, a novel ratiometric fluorescent probe based on CDs@Eu/GMP ICP nanoparticles was developed for the detection of Aβ monomer in rat as a biomarker for Alzheimer's disease (AD) by fully exploring the competitive coordination interaction and by taking advantage of excellent optical property of carbon dots sensitized lanthanide infinite coordination polymer (ICP) nanoparticles. The carbon dots (CDs) with abundant functional groups were encapsulated into Eu/GMP ICPs through self-adaptive chemistry, which could not only sensitize the red fluorescence of Eu/GMP ICPs effectively, but also act as an internal reference for self-correction. In the absence of Cu²⁺, the as-formed CDs@Eu/GMP ICPs exhibited the characteristic emission of CDs at 400 nm and strong emission of Eu³⁺ at 592 nm, 615 nm, 650 nm and 694 nm. With the addition of Cu²⁺, the red fluorescence of Eu³⁺ decreased due to the coordination interaction between CDs and Cu²⁺, thus destroyed the antenna effect. After the subsequent addition of Aβ monomer, the specific binding occurred between Cu²⁺ and Aβ monomer, and then the red fluorescence of Eu³⁺ restored again. During this process, the fluorescence of CDs remained unchanged, thus could be used as an internal reference to cancel out the environmental fluctuation and was more adaptive for the detection of Aβ monomer in biological fluids. The method demonstrated here was highly sensitive, free from the interference of other species in rat brain, the in vivo analysis of Aβ monomer in CSF and different brain regions from normal rats and Alzheimer's rats could be realized, which was of great significance for better understanding the mechanism of AD and paving the way to understand the chemical essence involved in AD.

An ICT-based fluorescent probe with a large Stokes shift for measuring hydrazine in biological and water samples

As a strong reductant and highly active alkali, hydrazine (N₂H₄) has been widely used in chemical industry, pharmaceutical manufacturing and agricultural production. However, its high acute toxicity poses a threat to ecosystem and human health. In the present study, a ratiometric fluorescent probe for the detection of N₂H₄ was designed, utilizing dicyanoisophorone as the fluorescent group and 4-bromobutyryl moiety as the recognition site. 4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl) phenyl 4-brobutanoate (DDPB) was readily synthesized and could specially sense N₂H₄ via an intramolecular charge transfer (ICT) pathway. The cyclization cleavage reaction of N₂H₄ with a 4-bromobutyryl group released phenolic hydroxyl group and reversed the ICT process between hydroxy group and fluorophore, turning on the fluorescence in the DDPB-N₂H₄ complexes. DDPB exhibits a low cytotoxicity, reasonable cell permeability, a large Stokes shift (186 nm) and a low detection limit (86.3 nM). The quantitative determination of environmental water systems and the visualization fluorescence of DDPB test strips provides a strong evidence for the applications of DDPB. In addition, DDPB is suitable for the fluorescence imaging of exogenous N₂H₄ in HeLa cells and zebrafish.

Competitive redox reaction of Au-NCs/MnO2 nanocomposite: Toward colorimetric and fluorometric detection of acid phosphatase as an indicator of soil cadmium contamination

In this study, by rational regulating the competitive redox reaction of Au-NCs/MnO₂ nanocomposite between the dye indigo carmine (IC) and the enzymatic product L-ascorbic acid (AA), we have established a colorimetric and fluorometric double-channel responsive assay for acid phosphatase (ACP), which could serve as an indicator of soil cadmium (Cd) contamination. Initially, the gold nanoclusters (Au-NCs) were added to the suspension of MnO₂ nanosheets to form Au-NCs/MnO₂ nanocomposite with enhanced oxidative degradation ability. When IC was subsequently added, the blue color of IC faded due to oxidative degradation, and the mixture showed the yellow color of Au-NCs/MnO₂ nanocomposite. Meanwhile, based on the inner filter effect (IFE), the fluorescence of Au-NCs was suppressed by MnO₂ nanosheets during this process. However, with the presence of AA, hydrolyzed from L-ascorbic-2-phosphate (AAP) by ACP, the MnO₂ nanosheets in Au-NCs/MnO₂ nanocomposite were reduced to Mn²⁺ immediately. As a consequence, IC remained its blue color, in the meantime, the fluorescence of Au-NCs recovered, which essentially constituted a new mechanism for ACP detection with colorimetric and fluorometric double-channel response. With the method we developed, soil ACP activity can either be directly visualized by bare eyes or detected reliably through double channels. Furthermore, the dynamic changes of ACP activity during soil Cd contamination could also be monitored; the sharp increase of ACP activity at an appropriate time point could serve as a unique alarm for cadmium (Cd) contamination in soil, which is of great importance for soil quality evaluation and ecological risk assessment.

A sensitive fluorescence assay of organophosphorus pesticides using acetylcholinesterase and copper-catalyzed click chemistry

Organophosphorus pesticides (OPs) are widely used in agricultural fields, but exhibit high toxicity to human beings. A sensitive fluorescence assay for organophosphorus pesticides was developed using the inhibition of acetylcholinesterase (AChE) activity and the copper-catalyzed click chemical reaction. In the click reaction, two hybridized DNA probes can be ligated with copper ions, inducing a fluorescence quenching during the strand displacement reaction. AChE can hydrolyze acetylthiocholine (ATCh) to form thiocholine (TCh) which contains a thiol group. TCh will react with copper ions, blocking the click reaction and a high fluorescence signal is observed. But in the presence of OPs, the activity of AChE is inhibited, releasing a high concentration of copper ions that catalyze the click chemical reaction and resulting in decreased fluorescence signals. Taking advantage of the copper-mediated signal amplification effect, the sensitivity was improved. This assay has also been applied to detect OPs in river water samples with satisfactory results, which demonstrates that the method has great potential for practical applications in environmental protection and food safety fields.

Synthesis of nitrogen-doped graphene quantum dots (N-GQDs) from marigold for detection of Fe3+ ion and bioimaging

Graphene quantum dots (GQDs) are synthesized by the method of high-temperature pyrolysis from marigold granules and subsequently nitrogen-doped graphene quantum dots (N-GQDs) are synthesized from ethylenediamine by hydrothermal treatment, which shows a strong blue emission with 7.84% quantum yield (QY). This will be used in detection of Fe³⁺ in water environments and the field of bioimaging.

Recent advances in functionalized MnO2 nanosheets for biosensing and biomedicine applications

As one kind of redox active layered transition-metal dioxide nanomaterials, single-layer manganese dioxide (MnO₂) nanosheets have gained significant research attention in the fields of biosensing and biomedicine because of their large surface area, intense and broad optical absorption, strong oxidation ability, catalytic activity, and robust mechanical properties. This review provides a brief overview of the recent advances in the development of MnO₂ nanosheet-based biosensors, bioimaging as well as drug delivery for cancer therapy. The methodologies for the preparation of MnO₂ nanosheets are summarized, followed by an introduction of the nanostructure and properties of MnO₂ nanosheets. Special attention is paid to their applications in biosensing, bioimaging and cancer therapy. Future perspectives and the challenges of high-performance MnO₂ nanosheets are also discussed.

Rational design of an ionic liquid dispersive liquid–liquid micro-extraction method for the detection of organophosphorus pesticides

In this study, a functionalized ionic liquid (IL), [MimCH₂COOCH₃][NTf₂] was rationally designed and explored as an extraction solvent in dispersive liquid–liquid microextraction (DLLME) combined with ultra-high performance liquid chromatography (UHPLC) for the sensitive determination of organophosphorus pesticides (OPs).

1-Naphthyl acetate: A chromogenic substrate for the detection of erythrocyte acetylcholinesterase activity

Erythrocyte acetylcholinesterase (AChE) is a preferred biomarker for the detection of organophosphorus poisoning. Acetylthiocholine (ATCh) is the most popular substrate for the detection of AChE activity. However, oximolysis is a prominent feature with ATCh. In this context, we have searched alternative substrates for AChE using in silico tools for screening of a better substrate. The in silico approach was performed to understand the fitness and the Total Interaction Energy (TIE) of substrates for AChE. The alternative substrates for AChE were screened in terms of high Goldscore and favorable TIE in comparison to acetylcholine (ACh)-AChE complex and other relevant esterases. Among the screened substrates, 1-Naphthyl acetate (1-NA) exhibited the most favorable interaction with AChE in terms of highest TIE and corresponding high Goldscore. The Molecular Dynamic (MD) simulation of the 1-NA-AChE complex showed a stable complex formation over a period of 5 ns. The results obtained in the in silico studies were validated in vitro using pure erythrocyte AChE and hemolysate. We observed 1-NA to be a better alternative substrate for AChE than ATCh in terms of lower Km value. Its specificity appeared at least similar to ATCh. Therefore, we propose that 1-NA can be an attractive chromogenic substrate for the measurement of AChE activity, and it possess the potential to detect organophosphorus pesticide (OP) poisoning.

Exploration of fluorescent organotin compounds of α-amino acid Schiff bases for the detection of organophosphorous chemical warfare agents: quantification of diethylchlorophosphate

Fluorescent Schiff base organotin probes for the detection of chemical warfare agents.

An on–off–on gold nanocluster-based fluorescent probe for sensitive detection of organophosphorus pesticides

In this study, a highly sensitive fluorescent probe based on bovine serum protein-protected gold nanoclusters (BSA-AuNCs) was developed for the determination of organophosphorus pesticides (OPs).