Fluorometric "AND" logic gate for detection of tyramine and tyrosinase based on in-situ formation of silicon-containing nanoparticles.

BACKGROUND: Tyramine is an important index of food freshness degree, and tyrosinase that can specifically oxidized monophenolamine to catecholamine plays a crucial part in the occurrence and development of melanin-related skin diseases. Therefore, it is crucial to develop sensitive and efficient methods for the detection of tyramine and tyrosinase. RESULTS: In this work, encouraged by tyrosinase-triggered specific oxidation of tyramine to dopamine and the unique fluorescent reaction between dopamine and amino silane, we have developed a one-step synthetic strategy of silicon containing nanoparticles (Si CNPs) for "turn-on" detection of tyramine and tyrosinase. The Si CNPs formed with thoroughly studied mechanism exhibit uniform structure and robust yellow-green fluorescence. The low detection limits for tyramine (1.87 µM) and tyrosinase (0.0029 U/mL) demonstrate admirable sensitivity outstripping most methods. The proposed assay achieves satisfactory results in the determination of tyramine and tyrosinase activity in real samples. Furthermore, we leverage this new fluorescent assay to enable the fabrication of an "AND" Boolean logic gate. SIGNIFICANCE: The entire process can be completed at easily available temperature and pressure with rapid response, convenient operation and visual observation. This fluorescent assay featured with excellent sensitivity, selectivity and stability has considerable prospects in the application of biosensors and disease diagnosis.

Light-Triggered Signal Enhancement Strategy Integrated with a CRISPR/Cas13a-Based Assay for Ultrasensitive and Specific miRNA Detection.

The development of facile, accurate, and affordable assays for microRNAs (miRNAs) in early cancer is greatly desirable but encounters an obstacle due to low cellular abundance in biofuids. In this study, we present a novel approach called a light-triggered exponential amplification strategy coupled with a CRISPR/Cas13a-based diagnostic system (LEXPA-CRISPR), which directly transduces rare miRNA targets into photocontrolled signal enhancement response. This innovative platform leverages trans-cleavage of CRISPR/Cas13a, activated by the miRNA target, to cleave specific RNA fragments within the MB@PC-NAC assembly, thus releasing free PC-single-stranded DNA (PC-ssDNA) that is modified by a photocleavable linker (PC linker). UV irradiation is further employed toward the photoresponsive PC-ssDNA, resulting in instantaneous generation of oligo with a new 5' phosphate group (Pho-ssDNA). The Pho-ssDNA serves as a trigger for rolling circle amplification (RCA) reaction, which generates thousands of long ssDNA repeats of diverse lengths with a strong fluorescence signal. Through optimization, we achieved a detection limit of 1 fM for miR21 without the need for target amplification. Moreover, the programmable versatility of LEXPA-CRISPR is also demonstrated for miR17 determination only with simple modification of CRISPR RNA (crRNA) sequences. This proposed biosensor successfully monitored the levels of miR21 and miR17 in tumor cells, showing a satisfactory consistency with the standard qRT-PCR method. Conclusively, LEXPA-CRISPR represents a promising strategy for ultrasensitive miRNA detection. It combines the advantages of light-triggered signal amplification and robust collateral cleavage activity of Cas13a, making it an attractive tool for practical CRISPR-based diagnostics.

Clinical observation and influence on nutritional status of intensive nutritional nursing combined with 3-day dietary diary intervention in peritoneal dialysis patients.

BACKGROUND: Peritoneal dialysis is a commonly used treatment for chronic kidney failure patients. Studies have shown that long-term peritoneal dialysis can lead to various degrees of malnutrition. Therefore, it is of great significance to improve the nutritional conditions of patients with peritoneal dialysis. This retrospective cohort study aimed to evaluate the clinical effects of intensive nutritional nursing combined with a 3-day diet diary intervention on the nutritional condition of peritoneal dialysis patients. METHODS: In total, 163 patients were included in this study and, after 6 months of intervention, their nutritional and biochemical indicators, body weight, body mass index (BMI) and intake of dietary ingredients were analysed. RESULTS: After the intervention, patients' serum albumin, haemoglobin, prealbumin, body weight, BMI and cholesterol levels were significantly increased (p < 0.05). Also, the daily energy and protein intake were significantly increased, whereas phosphorus intake was decreased (p < 0.05). Of note, the effective rate of intervention was 63.8%, respectively. We also found that factors such as the patient's age, education degree, income level and peritoneal dialysis age were the risk factors associated with malnutrition. Moreover, patients younger than 55 years old, with dialysis age younger than 5 years, unmarried/divorced and high school graduates, had higher chances of effective intervention, whereas the possibility of effective intervention was lower when the per capita monthly household income was less than 4000 Yuan. CONCLUSIONS: In conclusion, intensive nutritional nursing combined with a 3-day dietary diary intervention can significantly improve the nutritional condition and optimise the diet structure of peritoneal dialysis patients with malnutrition. These findings provide evidence for healthcare providers to develop personalised interventions to address malnutrition in this population.

A one-tube dual-readout biosensor for detection of nucleic acids and non-nucleic acids using CRISPR-ALP tandem assay.

Clustered regularly interspaced short palindromic repeats (CRISPR)-based diagnostics have been considered a next-generation molecular diagnosis tool. Single-readout mode has been extensively employed in massive CRISPR/Cas12a-based biosensors. In this work, we propose a one-tube dual-readout biosensor (CRISAT) for the first time for the detection of ultrasensitive nucleic acids and non-nucleic acids developed by harnessing CRISPR-ALP tandem assay. In the presence of a target, Cas12a is activated to randomly cut the single-stranded hyDNA sequence of MB@hyDNA-cALP, thus releasing abundant alkaline phosphatase (ALP) in the supernatant solution. By using 4-aminophenol phosphate as the substrate of ALP, p-aminophenol is produced, which then reacts with N-[3-(trimethoxysilyl)propyl]ethylenediamine or diethylenetriamine to generate silicon-containing polymer carbon dots (Si PCDs) or polymer carbon dots (PCDs) in situ, which can be observed by the naked eye or detected using a fluorescent device in the same solution. Using this strategy, a fluorescence and colorimetry dual-readout nanoplatform for CRISPR-based biosensors can be rationally developed. We ascertain the applicability of CRISAT by detecting the SARS-CoV-2 pseudovirus, achieving superior sensitivity and specificity. With simple modification of crRNAs, the CRISAT platform can also be employed to detect monkeypox virus (MPXV) and non-nucleic acids of adenosine triphosphate (ATP). This work shows great potential for the detection of nucleic acids and non-nucleic acids.

Fluorescence detection of 4-nitrophenol and α-glucosidase activity based on 4-nitrophenol-regulated fluorescence of silicon nanoparticles.

A fluorescence assay for the detection of 4-nitrophenol (4-NP), α-glucosidase (α-Glu) activity and α-Glu inhibitors (AGIs) is developed based on the inner filter effect (IFE), a flexible and simple signal transfer strategy. In this assay, silicon nanoparticles (Si NPs) synthesized under mild and easily accessible conditions are employed as fluorescent indicators. 4-NP efficaciously quenches the fluorescence of Si NPs through the IFE at a very rapid rate, thus achieving 4-NP detection in a mix-to-read manner, which is suitable for on-site detection. The quenching mechanism has been comprehensively studied and confirmed. More significantly, based on the fact that 4-NP can be generated through α-Glu-catalyzed hydrolysis of 4-nitrophenyl-α-D-glucopyranoside (NPG), the fluorescence detection of α-Glu activity is legitimately achieved by employing NPG as the substrate. The linear ranges for 4-NP and α-Glu activity detection are 0.5-60 µM and 0.5-60 mU mL-1 with low detection limits of 0.074 µM and 0.094 mU mL-1, respectively. This method not only can preciously assay targets in real samples, but is also capable of screening AGIs as drugs as well as assessing their inhibition efficiency.

Malathion detection based on polydopamine enhanced oxidase-mimetic activity of palladium nanocubes.

Nowadays, fabricating simple and efficient pesticide detection methods become a research focus due to the great threat pesticide residues posed to human health and environment. Herein, we constructed a high-efficiency and sensitive colorimetric detection platform for malathion detection based on polydopamine-dressed Pd nanocubes (PDA-Pd/NCs). The Pd/NCs coated with PDA exhibited excellent oxidase-like activity, which was attributed to the substrates accumulation and accelerated electron transfer induced by PDA. What's more, we successfully achieved sensitive detection of acid phosphatase (ACP) using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, relying on the satisfactory oxidase activity from PDA-Pd/NCs. However, the addition of malathion could inhibit the activity of ACP and limit the production of medium AA. Therefore, we constructed a colorimetric assay for malathion based on PDA-Pd/NCs + TMB + ACP system. The wide linear range (0-8 µM) and low detection limit (0.023 µM) indicate excellent analytical performance, which is superior to most malathion analysis methods previously reported. This work not only provides a new idea for dopamine coated nano-enzyme to improve its catalytic activity, but also creates a new tactics for the detection of pesticides such as malathion.

Regulating the N Coordination Environment of Co Single-Atom Nanozymes for Highly Efficient Oxidase Mimics.

Single-atom catalysts with well-defined atomic structures and precisely regulated coordination environments have been recognized as potential substitutes for natural metalloenzymes. Inspired by the metal coordination structure of natural enzymes, we show here that the oxidase-like activity of single-atom Co catalysts greatly depends on their local N coordination around the Co catalytic sites. We synthesized a series of Co single-atom catalysts with different nitrogen coordination numbers (Co-Nx(C), x = 2, 3, and 4) and demonstrated that the oxidase-like activity of single-atom Co catalysts could be effectively tailored by fine-tuning the N coordination. Among the studied single-atom Co catalysts, the Co-N3(C) with three-coordinate N atoms shows the optimum oxygen adsorption structure and robust reactive oxygen species (ROS) generation, thus presenting the preferable oxidase-like catalytic activity. This work facilitates the future development of rational nanozyme designs for targeting reactions at the atomic level.

Platinum nanoparticles confined in metal-organic frameworks as excellent peroxidase-like nanozymes for detection of uric acid.

High levels of uric acid (UA) in humans can cause a range of diseases, and traditional assays that rely on uric acid enzymes to break down uric acid are limited by the inherent deficiencies of natural enzymes. Fortunately, the rapid development of nanozymes in recent years is expected to solve the above-mentioned problems. Hence, we used a host-guest strategy to synthesize a platinum nanoparticle confined in a metal-organic framework (Pt NPs@ZIF) that can sensitively detect UA levels in human serum. Unlike previously reported free radical-catalyzed oxidation systems, its unique electron transfer mechanism confers excellent peroxidase-like activity to Pt NPs@ZIF. In addition, UA can selectively inhibit the chromogenic reaction of TMB, thus reducing the absorbance of the system. Therefore, using the peroxidase-like activity of Pt NPs@ZIF and using TMB as a chromogenic substrate, UA can be detected directly without relying on natural enzymes. The results showed a relatively wide detection range (10-1000 µM) and a low detection limit (0.2 µM). Satisfactory results were also obtained for UA in human serum. This study with simple operation and rapid detection offers a promising method for efficiently detecting UA in serum.

Rational design and fabrication of MoSx nanoclusters decorated Mn0.3Cd0.7S nanorods with promoted interfacial charge transfer toward robust photocatalytic H2 generation.

In this work, we report a novel MoSx/Mn0.3Cd0.7S composite catalyst that has been designed and fabricated by in situ coupling MoSx nanoclusters with 1D Mn0.3Cd0.7S nanorods for photocatalytic H2 production. The catalyst features a 1D nanostructure with MoSx nanoclusters uniformly dispersed along the Mn0.3Cd0.7S nanorod. It was found that an intimate interface is built between MoSx nanoclusters and Mn0.3Cd0.7S nanorods thanks to the facile in situ photoreduction route, which contributes to a high-efficiency interfacial charge separation. The resulting MoSx/Mn0.3Cd0.7S photocatalyst shows a dramatically enhanced visible-light-driven photocatalytic H2 production activity compared with the control samples, owing to more efficient spatial charge separation as well as enriched active sites. This work is expected to provide an optimized structure model for rational design and constructing novel, inexpensive, efficient and stable cocatalyst/metal sulfide photocatalyst systems for H2 production.

CRISPR/Cas12a-Enabled Multiplex Biosensing Strategy Via an Affordable and Visual Nylon Membrane Readout.

Most multiplex nucleic acids detection methods require numerous reagents and high-priced instruments. The emerging clustered regularly interspaced short palindromic repeats (CRISPR)/Cas has been regarded as a promising point-of-care (POC) strategy for nucleic acids detection. However, how to achieve CRISPR/Cas multiplex biosensing remains a challenge. Here, an affordable means termed CRISPR-RDB (CRISPR-based reverse dot blot) for multiplex target detection in parallel, which possesses the advantages of high sensitivity and specificity, cost-effectiveness, instrument-free, ease to use, and visualization is reported. CRISPR-RDB integrates the trans-cleavage activity of CRISPR-Cas12a with a commercial RDB technique. It utilizes different Cas12a-crRNA complexes to separately identify multiple targets in one sample and converts targeted information into colorimetric signals on a piece of accessible nylon membrane that attaches corresponding specific-oligonucleotide probes. It has demonstrated that the versatility of CRISPR-RDB by constructing a four-channel system to simultaneously detect influenza A, influenza B, respiratory syncytial virus, and SARS-CoV-2. With a simple modification of crRNAs, the CRISPR-RDB can be modified to detect human papillomavirus, saving two-thirds of the time compared to a commercial PCR-RDB kit. Further, a user-friendly microchip system for convenient use, as well as a smartphone app for signal interpretation, is engineered. CRISPR-RDB represents a desirable option for multiplexed biosensing and on-site diagnosis.

Multienzyme Cascades Based on Highly Efficient Metal-Nitrogen-Carbon Nanozymes for Construction of Versatile Bioassays.

Distinguished by the coupled catalysis-facilitated high turnover and admirable specificity, enzyme cascades have sparked tremendous attention in bioanalysis. However, three-enzyme cascade-based versatile platforms have rarely been explored without resorting to tedious immobilization procedures. Herein, we have demonstrated that formamide-converted transition metal-nitrogen-carbon (f-MNC, M = Fe, Cu, Mn, Co, Zn) with a high loading of atomically dispersed active sites possesses intrinsic peroxidase-mimetic activity following the activity order of f-FeNC > f-CuNC > f-MnNC > f-CoNC > f-ZnNC. Ulteriorly, benefitting from the greatest catalytic performance and explicit catalytic mechanism of f-FeNC, versatile enzyme cascade-based colorimetric bioassays for ultrasensitive detection of diabetes-related glucose and α-glucosidase (α-Glu) have been unprecedentedly devised using f-FeNC-triggered chromogenic reaction of 3,3',5,5'-tetramethylbenzidine as an amplifier. Notably, several types of α-Glu substrates can be effectively utilized in this three-enzyme cascade-based α-Glu assay, and it can be further employed for screening α-Glu inhibitors that are used as antidiabetic and antiviral drugs. These versatile assays can also be extended to detect other H2O2-generating or -consuming biomolecules and other bioenzymes that are capable of catalyzing glucose generation procedures. These nanozyme-involved multienzyme cascades without intricate enzyme-engineering techniques may provide a concept to facilitate the deployment of nanozymes in celestial versatile bioassay fabrication, disease diagnosis, and biomedicine.

Emerging interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic elements for electrocatalytic applications.

Palladium (Pd)-based nanomaterials have been identified as potential candidates for various types of electrocatalytic reaction, but most of them typically exhibit unsatisfactory performances. Recently, extensive theoretical and experimental studies have demonstrated that the interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic atoms (H, B, C, N, P, S) has a significant impact on their electronic structure and thus leads to the rapid development of one kind of promising catalyst for various electrochemical reactions. Considering the remarkable progress in this area, we highlight the most recent progress regarding the innovative synthesis and advanced characterization methods of nonmetallic atom-doped Pd-based nanomaterials and provide insights into their electrochemical applications. What's more, the unique structure- and component-dependent electrochemical performance and the underlying mechanisms are also discussed. Furthermore, a brief conclusion about the recent progress achieved in this field as well as future perspectives and challenges are provided.

Peroxidase-like activity of Ru-N-C nanozymes in colorimetric assay of acetylcholinesterase activity.

Herein, the Ru-N-C nanozymes with abundant active Ru-Nx sites have been successfully prepared by pyrolyzing Ru(acac)3 trapped zeolitic-imidazolate-frameworks (Ru(acac)3@ZIF-8). Taking advantages of the remarkable peroxidase-mimicking activity, outstanding stability and reusability of Ru-N-C nanozymes, a novel biosensing system with explicit mechanism is strategically fabricated for sensitively determining acetylcholinesterase (AChE) and tacrine. The limit of detection for AChE activity can achieve as low as 0.0433 mU mL-1, and the IC50 value of tacrine for AChE is about 0.190 µmol L-1. The robust analytical performance in serums test verifies the great application potential of this assay in real matrix. Furthermore, "INH" and "IMPLICATION-AND" logic gates are rationally constructed based on the proposed colorimetric sensor. This work not only provides one sustainable and effective avenue to fabricate Ru-N-C-based peroxidase mimic with high catalytic performance, and also gives new impetuses for developing novel biosensors by applying Ru-N-C-based enzyme mimics as substitutes for the natural enzyme.

Manganese-doped iron coordination polymer nanoparticles with enhanced peroxidase-like activity for colorimetric detection of antioxidants.

A convenient and sensitive antioxidant assay with high performance is essential for assessing food quality and monitoring the oxidative stress level of biological matrices. Although coordination polymer nanoparticles (CPNs)-based nanozymes have emerged as candidates in the analytical field, strategies to improve the catalytic activity of CPNs have been scarcely revealed and studied. Herein, we demonstrate a manganese (Mn) doping strategy to enhance the peroxidase-mimetic activity of Fe-based CPNs. By tuning the Mn doping amounts and selecting 2,5-dihydroxyterephthalic acid (H4DHTP) as ligands, the produced nanozymes in amorphous state followed the catalytic activity order of Fe5Mn-DHTP > Fe8Mn-DHTP > Fe2Mn-DHTP > Fe-DHTP > Mn-DHTP. Ulteriorly, benefitting from the best catalytic performance and definite catalytic mechanism of Fe5Mn-DHTP, versatile colorimetric assays for ultrasensitive detection of one exogenous antioxidant (ascorbic acid, AA) and two endogenous antioxidants (glutathione, GSH; cysteine, Cys) have been deftly devised based on the inhibition of the 3,3',5,5'-tetramethylbenzidine chromogenic reaction in presence of H2O2. It was found that mercaptan (GSH and Cys) and AA exhibited different inhibition mechanisms. Practically, such a colorimetric assay was viable to determine the total antioxidant capacity of drugs and foods with desirable results. This work proposes a feasible strategy for embellishing CPN nanozymes used for designing sensitive and convenient assays for various antioxidants based on an explicit detection mechanism.

Colorimetric detection of acetylcholinesterase and its inhibitor based on thiol-regulated oxidase-like activity of 2D palladium square nanoplates on reduced graphene oxide.

A convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) and its inhibitor has been designed based on the oxidase-like activity of {100}-faceted Pd square nanoplates which are grown in situ on reduced graphene oxide (PdSP@rGO). PdSP@rGO can effectively catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) without the assistance of H2O2 to generate blue oxidized TMB (oxTMB) with a characteristic absorption peak at 652 nm. In the presence of AChE, acetylthiocholine (ATCh), a typical AChE substrate, is hydrolyzed to thiocholine (TCh). The generated TCh can effectively inhibit the PdSP@rGO-triggered chromogenic reaction of TMB via cheating with Pd, resulting in color fading and decrease in absorbance. Thus, a sensitive probe for AChE activity is constructed with a working range of 0.25-5 mU mL-1 and  a limit of detection (LOD) of 0.0625 mU mL-1. Furthermore, because of the inhibition effect of tacrine on AChE, tacrine is also detected through the colorimetric AChE assay system within the concentrations range 0.025-0.4 µM with a LOD of 0.00229 µM. Hence, a rapid and facile colorimetric procedure to sensitively detect AChE and its inhibitor can be anticipated through modulating the oxidase-like activity of PdSP@rGO. Colorimetric method for detection of AChE and its inhibitor is established by modulating the oxidase mimetic activity of {100}-faceted Pd square nanoplates on reduced graphene oxide (PdSP@rGO).

Ultrathin PdCu alloy nanosheet-assembled 3D nanoflowers with high peroxidase-like activity toward colorimetric glucose detection.

Enzyme-mimetic properties of nanomaterials can be efficiently tuned by controlling their size, composition, and structure. Here, ultrathin PdCu alloy nanosheet-assembled three-dimensional (3D) nanoflowers (Pd1Cux NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of H2O2, the as-synthesized Pd1Cux NAFs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to the oxidized form of TMB (oxTMB) with a characteristic absorption peak at 652 nm. Interestingly, Pd1Cux NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy. Additionally, different from 2D Pd nanosheets, the distinctive 3D superstructures are featured with rich approachable sites and proper layer spacing, which are in favor of fast mass transport and electron transfers during the catalytic process. Among the studied Pd1Cux NAFs, the Pd1Cu1.7 NAFs show the highest enzyme-like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93 ± 0.53 µM. This work provides an efficient avenue to fabricate PdCu NAF nanozymes in biosensing toward glucose detection. Two-dimensional (2D) PdCu ultrathin nanosheet-assembled 3D nanoflowers (Pd1Cux NAFs) with tunable surface composition exhibit substantially enhanced intrinsic peroxidase-like catalytic activities. The Pd1Cu1.7 NAFs are successfully used as peroxidase mimic catalyst for the colorimetric detection of glucose with low detection limit of 2.93 µM.

Inhibited oxidase mimetic activity of palladium nanoplates by poisoning the active sites for thiocyanate detection.

In this work, a novel convenient colorimetric method for sensitive detection of thiocyanate (SCN-) has been developed based on its suppression of the oxidase-like activity of palladium square nanoplates on reduced graphene oxide (Pd SP@rGO). SCN- can be adsorbed onto the surface of Pd SP@rGO via binding with Pd atoms and blocks the active sites that mimic oxidase, thus inhibiting the corresponding chromogenic reaction of 3,3',5,5'-tetramethylbenzidine, which has been comprehensively revealed by the UV-vis spectra and X-ray photoelectron spectra. The color fading exhibits SCN- concentration-dependent behavior and can be easily recorded by either UV-vis spectroscopy or naked-eye observation. Therefore, both quantitative detection via measurement of the decrease in absorbance and visual detection of SCN- can be achieved. Owing to the intrinsic amplification of signals by the oxidase-like activity of Pd SP@rGO without resorting to unstable and destructive H2O2, this assay is straightforward, robust and sensitive enough for the detection of SCN- in real samples. Furthermore, an "INH" logic gate is rationally constructed based on the proposed colorimetric SCN- sensor.

Light-responsive Au nanoclusters with oxidase-like activity for fluorescent detection of total antioxidant capacity.

A fluorescent assay for total antioxidant capacity (TAC) detection based on the light-responsive oxidase-like activity of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) has been developed. Thiamine (TH) as the peroxidase substrate usually works at alkaline conditions and thus limits its practical applications. Here, by utilization the light-responsive oxidase-like activity of BSA-AuNCs, TH is oxidized to fluorescent thiochrome under neutral condition in two minutes due to the single oxygen generated by BSA-AuNCs upon light irradiation. After the introduction of antioxidants into the BSA-AuNCs-TH system, the formation of thiochrome is inhibited resulting in the fluorescence decrease. On the basis of the above facts, BSA-AuNCs-TH-based assay has been fabricated and applied successfully to detect antioxidants and the TAC of vitamin C tablets as well as some commercial fruit juice with satisfied results. This work may provide novel insights into developing light-responsive nanozymes-based fluorescent assays.

Alkaline Phosphatase-Triggered in Situ Formation of Silicon-Containing Nanoparticles for a Fluorometric and Colorimetric Dual-Channel Immunoassay.

Enzyme-triggered in situ chromogenic and/or fluorogenic reactions under accessible conditions are significant for developing enzyme activity and related spectroscopic assays. Here, we describe a facile one-pot synthetic strategy to prepare silicon-containing nanoparticles with yellow-green fluorescence and orange-red color by mixing N-[3-(trimethoxysilyl)propyl]ethylenediamine and p-aminophenol (AP) in aqueous solution at a mild temperature. Encouraged by the AP-regulated simple synthetic procedure and the generation of AP from alkaline phosphatase (ALP)-catalyzed hydrolysis of 4-aminophenol phosphate (APP), a fluorometric and colorimetric dual-readout ALP activity assay can be rationally envisioned and developed by employing APP as the substrate. In the wake of the good analytical performance of such ALP activity assay and its successful combination with enzyme-linked immunosorbent assay (ELISA), corresponding fluorometric and colorimetric dual-readout ALP-based ELISA has been constructed for highly sensitive and quantitative determination of human prostate-specific antigen (PSA), the key biomarker of prostate cancer in human serum. The convincing performance in evaluating the PSA level in serologic tests unambiguously reveals the great potential of our proposed fluorometric and colorimetric dual-channel immunoassay in early clinical diagnosis by monitoring disease biomarkers.

Colorimetric determination of the activity of alkaline phosphatase by exploiting the oxidase-like activity of palladium cube@CeO2 core-shell nanoparticles.

Core-shell palladium cube@CeO2 (Pd cube@CeO2) nanoparticles are shown to display oxidase-like activity. This is exploited in a method for determination of the activity of alkaline phosphatase (ALP). The Pd cube@CeO2 nanoparticles were thermally synthesized from Ce(NO3)3, L-arginine and preformed Pd cube seeds in water. The Pd cube@CeO2 nanoparticles catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen. This results in the formation of oxidized TMB (oxTMB) with an absorption peak at 652 nm. Ascorbic acid (AA) is generated from the hydrolysis of L-ascorbic acid 2-phosphate (AAP) catalyzed by ALP. It can reduce oxTMB to TMB, and this results in a decrease of the absorbance. The method allows for quantitative determination of the activity of ALP in the range from 0.1 to 4.0 U·L-1 and with a detection limit down to 0.07 U·L-1. Endowed with high sensitivity and selectivity, the assay can quantify ALP activity in biological system with satisfactory results. Graphical abstractSchematic illustration of Pd cube@CeO2 core-shell nanoparticles for colorimetric determination of alkaline phosphatase.