Restoring the Oxidase-Like Activity of His@AuNCs for the Determination of Alkaline Phosphatase

Colorimetric detection of alkaline phosphatase based on the off-on effect of light-responsive oxidase mimicking activity of covalent organic framework (Cu-TpBpy-COF) under near-neutral condition

A colorimetric strategy has been developed for the detection of alkaline phosphatase (ALP) activity based on the off-on effect of the catalytic activity of light-responsive oxidase mimics covalent organic framework (Cu-TpBpy-COF) in near-neutral condition. Cu-TpBpy-COF can effectively catalyze the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen to form a blue oxidized product (oxTMB) with an absorption peak at 652 nm. Cu2+ is the active center of Cu-TpBpy-COF and pyrophosphate (PPi) can form a complex with Cu2+ to weaken the catalytic activity of Cu-TpBpy-COF. In the presence of ALP, PPi is hydrolyzed into orthophosphates (Pi) with low affinity to Cu2+, thus resulting in absorbance restoration. The absorbance at 652 nm is related to ALP activity in the linear range 10-150 U·L-1 with a detection limit of 7.17 U·L-1. The recoveries of ALP in serum samples are in the range 94.7~107.0% with relative standard deviations (RSD) lower than 5%. The decisive role of Cu2+ on the enhancing catalytic activities of Cu-TpBpy-COF in neutral condition was verified by TpBpy-COF and TpBD-COF as controls, in which the main difference between them is that TpBpy-COF contains pyridine nitrogen. Upon Cu2+ modification, Cu-TpBpy-COF has better catalytic activity than TpBpy-COF in a broader pH range because of the in situ generation of Cu+ under irradiation.

Platinum nanoflowers stabilized with aloe polysaccharides for detection of organophosphorus pesticides in food

Organophosphorus pesticides can inhibit the activity of acetylcholinesterase and cause neurological diseases. Therefore, it is crucial to establish an efficient and sensitive platform for organophosphorus pesticide detection. In this work, we extracted aloe polysaccharide (AP) from aloe vera with the number average molecular weight of 27760 Da and investigated its reducing property. We prepared aloe polysaccharide stabilized platinum nanoflowers (AP-Ptn NFs), their particle size ranges were 29.4-67.3 nm. Furthermore, AP-Ptn NFs exhibited excellent oxidase-like activity and the catalytic kinetics followed the typical Michaelis-Menten equation. They showed strong affinity for 3,3',5,5'-tetramethylbenzidine substrates. More importantly, we developed a simple and effective strategy for the sensitive colorimetric detection of organophosphorus pesticides in food using biocompatible AP-Ptn NFs. The detection range was 0.5 μg/L - 140 mg/L, which was wider than many previously reported nanozyme detection systems. This colorimetric biosensor had good selectivity and good promise for bioassay analysis.

A turn-on chemiluminescent assay for alkaline phosphatase using two-dimensional Fe-centered metal-organic frameworks as the signaling probe

Alkaline phosphatase (ALP) is an essential enzyme involved in cell phosphorus metabolism. Developing sensitive and accurate ALP quantitative assays is significant. In this study, a turn-on chemiluminescence (CL) analysis platform for the detection of ALP activity in human serum was established based on two-dimensional (2D) Fe-centered metal-organic frameworks with 1,3,5-benzene tricarboxylic acid as ligands (denoted as 2D Fe-BTC). The 2D Fe-BTC as the signaling probe reacts with ascorbic acid forming reduced Fe-BTC which catalyzes the luminol CL reaction producing a strong CL signal. The 2D Fe-BTC-based luminol CL reaction exhibited good CL responses when the concentration of ascorbic acid was in the range of 5-500 nM. By employing magnesium ascorbyl phosphate (MAP) as the substrate which can be hydrolyzed by ALP to generate ascorbic acid, a turn-on CL assay for the detection of ALP was established. Under optimal conditions, as low as 0.00046 U L-1 of ALP could be sensitively detected with a linear range of 0.001-0.1 U L-1. ALP in human serum can be detected after a simple dilution process without any other pretreatment.

A ratiometric fluorescence method based on nitrogen-doped carbon quantum dots for the determination of the activity of alkaline phosphatase

Herein, a simple and sensitive ratiometric fluorescence sensing platform to detect alkaline phosphatase (ALP) activity is developed on the basis of yellow fluorescent nitrogen-doped carbon quantum dots (YNCDs). The hydrolysis of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA) is catalyzed by ALP. Then, AA will react with o-phenylenediamine (OPD) to form 3-(1,2-dihydroxyethyl)furo[3,4b]-quinoxaline (QXD) which is a blue fluorescent quinoxaline derivative with emission at 435 nm in the presence of Cu²⁺. YNCDs have yellow fluorescence emission at 555 nm, and can maintain stable in QXD reaction system. Therefore, by utilizing the fluorescence of YNCDs at 555 nm as reference signal and the fluorescence of QXD at 435 nm as report signal, we can detect the ALP activity by monitoring the fluorescence ratio (F₄₃₅/F₅₅₅). The linear range is 0.5-5 U/L, and the limit of detection is 0.14 U/L. An application of this method for the analysis of ALP in human serum has given satisfactory results. A ratiometric fluorescent nanoprobe for ascorbic acid and alkaline phosphatase detection with excellent biocompatible and high sensitivity was successfully constructed based on YNCDs and QXD.

A novel electrochemical platform for assay of alkaline phosphatase based on amifostine and ATRP signal amplification

Alkaline phosphatase (ALP), an important hydrolase involved in dephosphorylation, is a common clinical indicator of many diseases. In the present study, we constructed a novel electrochemical sensor using amifostine as the substrate of ALP and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a signal amplification strategy for sensitive determination of ALP activity. In particular, in the presence of ALP, the phosphate group of amifostine was hydrolyzed to form a sulfhydryl group, which could attach to a gold electrode via a sulfur-gold bond. Then, the initiator α-bromophenylacetic acid (BPAA) was linked to the hydrolysis product of amifostine through an amide bond, resulting in the production of electroactive polymer chains on the gold electrode by the monomer ferrocenylmethyl methacrylate (FMMA) via ARGET ATRP. Under optimal parameters, the electrochemical sensor demonstrated a limit of detection (LOD) of 1.71 mU mL^-1 with a linear range of 5-100 mU mL^-1. In addition to satisfactory selectivity, the potential application of this approach for ALP activity detection in human serum samples was demonstrated. Due to its efficiency, simplicity of operation, and cost-effectiveness, the proposed electrochemical sensor has great promise as a universal method for ALP assays and inhibitor screening.

Electrochemical detection of alkaline phosphatase activity via atom transfer radical polymerization

Alkaline phosphatase (ALP) activity is a diagnostic indicator for a variety of clinical diseases. In this study, an electrochemical method for detecting ALP activity through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was developed. Specifically, 3-mercaptopropionic (MPA) was firstly fixed on the electrode through sulfur-gold bonding. Subsequently, α-bromophenylacetic acid (BPAA) as initiator was attached to MPA through the recognized carboxylate-Zr4+-phosphate chemistry. Finally, in the existence of ALP, L-Ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS) was hydrolyzed to produce ascorbic acid (AA) which participated in the ARGET ATRP reaction, grafting polymer containing plenty of ferrocene electroactive probes on the surface of electrode. Under optimal experimental conditions, this method had a linear scope of 20-200 mU mL-1, and a limit of detection (LOD) of 1.64 mU mL-1. In addition, the proposed method had good selectivity as well as anti-interference capability, with satisfactory results in inhibition rate and human serum experiments. By merits of good analytical performance, easy operation, and low cost, such a method for ALP activity detection has promising applications in ALP-related disease detection and inhibitor screening.