Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

A dual mode biosensor based on self-enhanced polyfluorene nanomaterial for fluorescence and electrochemiluminescence detection of Tau protein

Dual mode detection can overcome the poor anti-interference ability of single-mode detection, and greatly improve the detection accuracy. Fluorescence/electrochemiluminescence (FL/ECL) dual mode detection combines the advantages of FL and ECL, and has a promising application in bioanalysis. Common FL/ECL dual mode detection used different signal probes. Multiple signal probes inevitably have complex operation and uncontrollable differences between the two modes. In this work, poly [9,9-dioctylfluorenyl-2,7-diyl]-End-capped with 2,5-diphenyl-1,2,4-oxadiazole (PFO) was functionalized by sodium dodecyl sulfate (SDS) and polyethylenimine (PEI), and the resulting PFO-SDS-PEI nanoparticles (PSP NPs) exhibited excellent FL and ECL performance at the same time, so were creatively developed as mono-luminophore-based signal probe for FL/ECL dual-mode detection. The functional reagent SDS can significantly improve the water dispersion of luminophores, and PEI can not only provide amino functional groups for assembling biomolecules, but also significantly enhance the FL and ECL signals of the luminophores. Self-enhanced PSP NPs coupled strand displacement reaction (SDR) mediated by exonuclease Ⅲ (Exo Ⅲ) to achieve FL/ECL dual-mode detection of Tau protein, a biomarker of Alzheimer's disease (AD). The linear ranges for FL and ECL detection were 0.001-500 pg/mL and 0.00001-1.0 pg/mL and the limit of detections were 549.16 ag/mL and 5.45 ag/mL, respectively, showing good application potential. Self-enhanced PSP NPs provided an ideal mono-luminophore-based signal probe for FL/ECL dual-mode detection, and built a new method for detecting AD biomarker.

Electrochemical/fluorescent dual-mode aptasensor based on 3D porous AuNPs/MXene for detection of ultra-trace mercury (Hg2+)

In this work, the dual-mode aptasensor based on 3D porous AuNPs/MXene using "turn-on" electrochemical method and "turn-off" fluorescent strategy was fabricated. Here, 2D MXene was processed into 3D porous MXene by sacrificial polymethylmethacrylate (PMMA) spherical template. And the meteor hammer-like AuNPs which had good electrochemical properties and quenching effect on fluorescence was synthesized by single electrodeposition. Dual-signal labeled Nile Blue (NB) was in situ grafted to the Hg2+ aptamer ends of 3D porous AuNPs/MXene/GCE, and an efficient and sensitive signal interface was constructed to realize the sensitive detection of Hg2+. 3D porous AuNPs/MXene had the advantages of large specific surface area, excellent electron transmission performance and signal amplification. The experimental results indicated that this sensor exhibited high sensitivity to Hg2+ in both electrochemical and fluorescent sensing, with detection limits of 2.69 fM and 1.60 fM, respectively. Further, the dual-mode aptasensor can ensure the detection accuracy and target quantization. The dual-mode aptasensor has been successfully applied to the ultra-trace detection of Hg2+ in actual water samples, which shows the potential of aptamer sensor in detecting heavy metal ions in environmental monitoring.

In situ developed NiCo2O4-Ti3C2Tx nanohybrid towards non-enzymatic electrochemical detection of glucose and hydrogen peroxide

Owing to the adverse consequences of excess glucose (Glu) and hydrogen peroxide (H2O2) on humans, it is imperative to develop an electrochemical sensor for detection of these analytes with good selectivity and sensitivity. Herein, a nanohybrid comprising nickel cobaltite nanoparticles (NiCo2O4 NPs) embedded on conductive Ti3C2Tx nanosheets (NSs) has been prudently designed and employed for the electrochemical detection of Glu and H2O2. The developed nanohybrid has been systematically characterized using morphological and spectral techniques, and then immobilized on a glassy carbon electrode (GCE). Under optimized conditions, the developed NiCo2O4-Ti3C2Tx/GCE based electrochemical sensor has demonstrated an impressive analytical response towards Glu and H2O2 with good sensitivity and selectivity. The non-enzymatic sensor has demonstrated a broad linear range from 30 μM to 1.83 mM for Glu, and two linear ranges of 20-100 μM and 100 μM-2.01 mM for H2O2. The sensor has exhibited limits of detection (LOD) of 9 μM and 6 μM with sensitivities of 101.2 μA μM-1 cm-2 and 107.03 μA μM-1 cm-2, respectively, for Glu and H2O2 detection. The impressive analytical performance of the fabricated sensor in terms of linear range, LOD and sensitivity are ascribed to the (i) enhanced conductivity of Ti3C2Tx NSs, (ii) mediated electrocatalytic activity of NiCo2O4 NPs and (iii) large number of catalytically active sites on the NiCo2O4-Ti3C2Tx heterostructure. Notably, the NiCo2O4-Ti3C2Tx/GCE has demonstrated impressive stability and reproducibility, which is mainly due to the in situ uniform growth of NiCo2O4 NPs over Ti3C2Tx NSs.

Time-Resolved Levodopa Cascade Polymerization Tuned by Bimetallic MOF Fluorescent Nanozyme and Boric Acid for Butyrylcholinesterase Activity Dual-Mode Assay

A ratiometric fluorescence-photothermal dual-mode assay method is constructed for the detection of butyrylcholinesterase (BChE) activity based on time-resolved levodopa (L-DOPA) cascade polymerization. First, a newly designed bimetallic metal-organic framework (MOF), Eu/Co-DPA (DPA: pyridine-2,6-dicarboxylic acid), is screened out as a fluorescent nanozyme with high catalytic activity and superior luminescence properties. In the presence of boric acid (BA), L-DOPA forms BA-esterified L-DOPA, which is catalyzed by Eu/Co-DPA to form the oligomers with strong blue fluorescence. Meanwhile, the red fluorescence of Eu/Co-DPA is quenched by the oligomers, generating a sensitive turn-on/off ratiometric fluorescence response. As polymerization time increases, Eu/Co-DPA cleaves the borate ester bonds to expose the catechol structures of the oligomers, which facilitates the further oxidation and polymerization of the oligomers, promoting the formation of poly(L-DOPA) nanoparticles with a high photothermal conversion efficiency (30.33%). Then, by using thiocholine (butyrylthiocholine enzymolysis product) to inhibit the catalytic activity of Eu/Co-DPA, BChE activity is detected through the change in fluorescence and photothermal dual signals. Both assay modes have low detection limits (0.021 and 0.024 U L-1) and high accuracy (93.3-105.3% recovery). The detection results of real human serum indicate that both assay modes show 100.0% agreement with the standard method. To our knowledge, this work first combines bimetallic MOFs and a BA regulator to tune the structure of L-DOPA polymers, providing a pathbreaking paradigm for preparing catecholamine-based fluorescence-photothermal organic polymers.

A novel near-infrared fluorescent probe for butyrylcholinesterase: Research for screening of natural anti-AD inhibitors

Elevated levels of butyrylcholinesterase (BuChE) have the potential to be predictive in the timely detection and diagnosis of Alzheimer's disease (AD). By inhibiting of BuChE activity can raise acetylcholine levels and intervene AD processes. Therefore, BuChE as an important factor in treatment AD has been given more and more attention in clinical studies. Given the facts above, in this study, for precise monitoring of BuChE level changes and screening for possible butyrylcholinesterase inhibitor (BuChEI) for AD diagnosis and therapy, a near-infrared (NIR) fluorescence probe (NFP-BuChE) was created. The probe exhibits excellent sensitivity and selectivity for BuChE. NFP-BuChE has been successfully applied to the detection of endogenous BuChE levels in live cells, and we successfully constructed a screening system for BuChEI on cells and a novel natural efficient BuChEI (matrine) was discovered and identified, which significantly reduced BuChE activity and thus alleviated AD symptoms. Most importantly, for the first time, we measured the changes of BuChE levels in zebrafish (0-4 days) after fertilization, various organs of zebrafish, and AD zebrafish modeled by different concentrations of AlCl3 by NFP-BuChE, and at the same time, we also validated the inhibitory effect of matrine on BuChE by NFP-BuChE in zebrafish. In addition, NFP-BuChE has also been successfully used to measure the changes of BuChE levels in the brains of AD mice. These findings imply that NFP-BuChE is a potentially useful molecular tool for screening possible natural BuChEI quickly and for monitoring changes in BuChE activity, and it is expected that more value will be explored in mice. In addition, matrine and its derivatives are promising options for future Alzheimer's disease treatments.

Butyrylcholinesterase-Activated Near-Infrared Fluorogenic Probe for In Vivo Theranostics of Alzheimer's Disease

Butyrylcholinesterase (BChE) is a promising biomarker and effective therapeutic target for Alzheimer's disease (AD). Herein, we designed a BChE-activated near-infrared (NIR) probe, DTNP, which could be activated by BChE and inhibit its enzymatic activity. DTNP is composed of a cyclopropane moiety as the recognition unit, a NIR fluorophore hemicyanine as the NIR reporter, and a BChE inhibitor as the therapeutic unit. DTNP specifically binds BChE with high sensitivity and exhibits strong "turn-on" NIR fluorescence as well as nerve cell protection. In vivo imaging shows DTNP has favorable blood-brain barrier permeability and long-term tracking ability with preliminary competence in AD diagnosis. DTNP can significantly inhibit BChE activity, promote the release of ACh, and rescue learning deficits and cognitive impairment. Therefore, DTNP, the first reported and partially validated theranostic probe for the detection of BChE in AD, may provide a foundation and inspiration for imaging and therapy in AD.

In situ detection of dopamine in single living cells by molecularly imprinted polymer-functionalized nanoelectrodes

In situ detection of dopamine (DA) at single-cell level is critical for exploring neurotransmitter-related biological processes and diseases. However, the low content of DA and a variety of distractors with similar oxidation potentials as DA in cells brought great challenges. Here, a sensitive and specific electrochemical nanosensor was proposed for in situ detection of DA in single living cells based on nanodiamond (ND) and molecularly imprinted polymer (MIP)-functionalized carbon fiber nanoelectrode (ND/MIP/CFNE). Due to its excellent electrocatalytic property, ND was modified to the surface of CFNE based on amide bonding. Compared with bare CFNE, ND-modified CFNE can enhance oxidation currents of DA by about 4-fold, improving signal-to-noise ratio and detection sensitivity. MIP was further electropolymerized on the surface of nanoelectrodes to achieve specific capture and recognition of DA, which could avoid the interference of complex matrix and analogs in cells. Taking advantage of the precise positioning capability of a single-cell analyzer and micromanipulator, ND/MIP/CFNE could be precisely inserted into different locations of single cells and monitor oxidation signal of DA. The concentration of DA in the cytoplasm of single pheochromocytoma (PC12) cell was measured to be about 0.4 μM, providing a sensitive and powerful method for single-cell detection. Furthermore, the nanoelectrodes can monitor the fluctuation of intracellular DA under drug stimulation, providing new ideas and methods for new drug development and efficacy evaluation.

Development of an activity-based ratiometric electrochemical probe of the tumor biomarker γ-glutamyl transpeptidase: Rapid and convenient sensing in whole blood, urine and live-cell samples

γ-Glutamyl transpeptidase (GGT) is a key biomarker for cancer diagnosis and post-treatment surveillance. Currently available methods for sensing GGT show high potential, but face certain challenges including an inability to be used to directly sense analytes in turbid biofluid samples such as whole blood without tedious sample pretreatment. To overcome this issue, activity-based electrochemical probes (GTLP and GTLPOH) were herein developed for a convenient and specific direct targeting of GGT activity in turbid biosamples. Both probes were designed to have GGT catalyze the hydrolysis of the gamma-glutamyl amide moiety of the probe, and result in a self-immolative reaction and concomitant ejection of the masked amino ferrocene reporter. The GTLPOH probe, delivered distinctive key results including high sensitivity, high affinity, a wide detection range of 2-100 U/L, and low LOD of 0.38 U/L against GGT. This probe delivered a precise target for sensing GGT and was free of interference from other electroactive biological species. Furthermore, the GTLPOH probe was employed to monitor and quantify the activity of GGT on the surfaces of tumor cells. The designed sensing method was also validated by the direct quantitative measurement of GGT activity in whole blood and urine samples, and the results were found to be consistent with those of the standard fluorometric assay kit. Thus, GTLPOH is of great significance for its promise as a point-of-care tool for early-stage cancer diagnosis as well as a new drug screening method.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

A novel near-infrared fluorescent probe for high-sensitivity detection of butyrylcholinesterase in various pathological states

Butyrylcholinesterase (BChE) is a crucial hydrolytic enzyme predominantly synthesized in the liver, playing a significant role in conditions like liver disorders, diabetes, Alzheimer's disease, and fat metabolism regulation. This study aims to address the current limitations in visualizing BChE activity in diseases at various states by introducing an ultra-sensitive near-infrared fluorescent probe, FDCM-BChE. The probe was engineered to have several properties, such as a large Stokes shift, rapid response time, high stability, excellent selectivity, and low detection limits. We validated the efficacy of FDCM-BChE in quantifying BChE activity in human serum and leveraged its low cytotoxicity for cellular imaging. The study revealed the downregulation of BChE activity in liver cancer and hepatic injury and the upregulation in diabetes. Thus, FDCM-BChE shows promise as a tool for specific applications, providing insights into diseases associated with BChE activity.

Thermodynamic Allosteric Switch-Actuated 3D DNA Nanomachine for Ultrasensitive Electrochemical/Fluorescent Dual-Mode Biosensing of a Transcription Factor

Herein, we reported an innovative thermodynamic allosteric switch-actuated 3D DNA nanomachine for selective, sensitive, and accurate electrochemical (EC)/fluorescent (FL) dual-mode biosensing of a microphthalmia-associated transcription factor (MITF). The thermodynamic allosteric switch was ingeniously customized as a hairpin probe (HP) that was in dynamic equilibrium but rapidly interconverting conformations. At the "inactive state", the MITF-binding region and the switch part were "sequestered". Upon the introduction of MITF, an MITF-HP complex promptly formed, and the equilibrium of HP thermodynamically inclined from the "inactive state" toward the "active state" conformation. Immediately, the exposed switch on HP effectively actuated the 3D DNA nanomachine and synchronously produced the restriction site for Nb.BbvCI nicking endonuclease. After the autonomous conveying of the 3D DNA nanomachine by means of the high-efficiency circularly nicking endonuclease signal amplification (NESA), not only was MB-S1 in the supernatant used for FL measurements but also MB-SP/MNs/S2 in the precipitate was adapted for EC analysis, significantly improving the utilization of output products derived from the 3D DNA nanomachine. Accordingly, benefiting from the efficient DNA nanomachine signal amplification manner and the self-calibration function of a dual-mode bioassay, the constructed biosensor exhibits superior sensitivity and accuracy for MITF determination.