Grafting of polymers via ring-opening polymerization for electrochemical assay of alkaline phosphatase activity

Butanol accelerated entropy-driven DNA walking machine for rapid and ultrasensitive determination of alkaline phosphatase activity

Alkaline phosphatase (ALP) as an important biomarker as well as an index for the pasteurization degree of dairy food. However, there is a dilemma between the sensitivity and time-cost of ALP determination based on nucleic acid amplification approach. Herein, an ultrasensitive and rapid detection method for the ALP assay was developed based on entropy-driven DNA machine. In our design, the ALP catalyzed dephosphorylation of detection probe, which inhibited the digestion effect of lambda exonuclease. The remaining probe as a linker to tether the walking strand proximity to the surface of track strand modified gold nanoparticle, activating entropy-driven DNA machine. Accompany with walking strand moving, a large amount of assembled dye-labelled strand dissociated from gold nanoparticle with fluorescence recovery. More importantly, to further improve the walking efficiency, butanol was introduced to accelerated the signal amplification at interface, which short the incubation time from several hours to 5 min. Under the optimum condition, the change of fluorescence intensity was proportion to the concentration of ALP in the range from 0.05 U L^-1 to 5 U L^-1 with an ultralow limit of detection of 2.07 × 10^-3 U L^-1 was achieved, which is superior to other reported methods. Furthermore, the proposed method also successfully applied for the spiked milk sample assay with satisfactory recovery in the range of 98.83%-103.00%. This work proposed a new strategy for the application of entropy-driven DNA machine in the field of rapid and ultrasensitive detection.

Controllable formation of polydopamine on carbon dots for ultrasensitive detection of alkaline phosphatase and ratiometric fluorescence immunoassay of benzocaine

Sensing alkaline phosphatase (ALP) activity with high sensitivity and accuracy is critical for both ALP-related health and food safety supervision and the development of ALP-triggered immunoassay platforms. Herein, an ultrasensitive ratiometric fluorescence (RF) sensing system based on the controllable formation of luminescent polydopamine and efficient quenching of carbon dots was proposed for the ALP activity assay, achieving quantitative detection in the range of 0.01-100 mU/L. Furthermore, this RF sensing system was integrated with an ALP-based ELISA platform to construct an RF-ELISA for benzocaine, a potentially abused anesthetic in edible fish, and ultrasensitive assay at the level of fg/mL was realized. This ratiometric strategy-based platform effectively shields various interferences through the self-calibration effect, thus providing more accurate and reliable quantification results. This study not only offers an efficient method for ultratrace detection of ALP and benzocaine but also proposes a universal platform for ultrasensitive detection of diverse targets in food analysis by replacing the recognition unit.

Dual signal amplified electrochemical aptasensor based on PEI-functionalized GO and ROP for highly sensitive detection of cTnI

Cardiac troponin I (cTnI) is considered as the gold standard for the diagnosis of acute myocardial infarction (AMI) because of its excellent specificity and sensitivity. Herein, a novel aptasensor based on the dual signal amplification strategy of Polyethyleneimine functionalized Graphene oxide (GO) and ring-opening polymerization (ROP) for the first time was successfully constructed to achieve high sensitivity detection of cTnI. Briefly, cTnI-aptamer 1 (Apt1) was immobilized on the surface of gold electrode by self-assembly of Au-S bonds to specifically capture cTnI. After specific recognition of cTnI, Apt2 coated PEI-functionalized GO composites acted as macroinitiators for the subsequent ROP reaction. Next, α-amino acid-N-carboxylic acid anhydride ferrocene derivatives (NCA-Fc), the monomer for ROP reaction, was added to the electrode surface. The combined application of PEI-functionalized GO and NCA-Fc better achieves the high sensitivity and signal amplification of the aptasensor. Under optimal conditions, the aptasensor exhibited a wide linear range of 10 fg mL^-1 to 10 ng mL^-1 and the limit of detection was 3.78 fg mL^-1. Moreover, this method displayed the advantages of good selectivity, simple operation and excellent stability. Meanwhile, the aptasensor had good accuracy and applicability even in real serum samples analysis, demonstrating its considerable application potential in biomedical assays.

A facile and sensitive magnetic relaxation sensing strategy based on the conversion of Fe3+ ions to Prussian blue precipitates for the detection of alkaline phosphatase and ascorbic acid oxidase

Herein, a novel magnetic relaxation sensing strategy based on the change in Fe³⁺ content has been proposed by utilizing the conversion of Fe³⁺ ions to Prussian blue (PB) precipitates. Compared with the common detection approach based on the valence state change of Fe³⁺ ions, our strategy can cause a larger change in the relaxation time of water protons and higher detection sensitivity since PB precipitate can induce a larger change in the Fe³⁺ ion concentration and has a weaker effect on the relaxation process of water protons relative to Fe²⁺ ions. Then, we employ alkaline phosphatase (ALP) as a model target to verify the feasibility and detection performance of the as-proposed strategy. Actually, ascorbic acid (AA) generated from the ALP-catalyzed L-ascorbyl-2-phosphate hydrolysis reaction can reduce potassium ferricyanide into potassium ferrocyanide, and potassium ferrocyanide reacts with Fe³⁺ to form PB precipitates, leading to a higher relaxation time. Under optimum conditions, the method for ALP detection has a wide linear range from 5 to 230 mU/mL, and the detection limit is 0.28 mU/mL, sufficiently demonstrating the feasibility and satisfactory analysis performance of this strategy, which opens up a new path for the construction of magnetic relaxation sensors. Furthermore, this strategy has also been successfully applied to ascorbic acid oxidase detection, suggesting its expansibility in magnetic relaxation detection.

A Novel Electrochemical Sensing Strategy Based on Poly (3, 4-ethylenedioxythiophene): Polystyrene Sulfonate, AuNPs, and Ag+ for Highly Sensitive Detection of Alkaline Phosphatase

Alkaline phosphatase (ALP) is a crucial marker for the clinical analysis and detection of many diseases. In this study, an accurate signal amplification strategy was proposed for the sensing and quantification of alkaline phosphatase using poly (3, 4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), gold nanoparticles (AuNPs), and Ag⁺. Signal amplification was achieved by the modification of PEDOT:PSS and AuNPs on glassy carbon electrodes. Atomic force microscopy was performed to characterize the morphology of the modified nanomaterials. To detect ALP, 1-naphthyl phosphate (1-NP) was used as the substrate, and alkaline phosphatase catalyzed 1-NP into 1-naphthol (1-N), which resulted in the reduction of Ag⁺ to Ag⁰ on the surface of the modified electrode (AuNPs/PEDOT:PSS/GCE). The deposition of Ag drastically enhanced the detection signal. Differential pulse voltammograms of 1-N, which is the enzymatic product from the ALP reaction with 1-NP, were recorded. In the linear range of 0.1-120 U L^-1, a quantitative analysis of alkaline phosphatase was achieved, with high sensitivity and a low detection limit of 0.03 U L^-1. Stable, selective, and reproducible electrochemical sensors were designed. Moreover, the proposed electrochemical sensor exhibited a prominent sensing performance in the spiked diluted human serum. Thus, the sensor can be used in numerous applications in alkaline phosphatase or other analyte detection.

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.

A label-free and modification-free ratiometric electrochemical strategy for enhanced natural enzyme detection using a bare electrode and nanozymes system

Ratiometric electrochemical assays have been demonstrated to be more sensitive and selective in various sensing events, mainly due to their affordable built-in correction and good self-reference capability. But it is known that complicated modification and labeling operations usually are necessary for the construction of ratiometric electrochemical assays, therefore is a hot and important issue needing consideration carefully. We herein report a new yet simple bare electrode-based ratiometric electrochemical bioassay to achieve sensitive and selective analysis of alkaline phosphatase (ALP), using a liquid phase system that contains CoOOH nanozymes and commercially available indicator substrate. This proposed bioassay works based on the ratiometric change of dual electrochemical signals, arising from an exclusive target ALP-triggered hydrolysis of electrochemical substrate p-nitrophenyl phosphate (PNPP). In this design, the two hydrolyzed products of electrochemically active p-nitrophenol (PNP) and electrochemically inactive phosphate anion (PO₄^3-) are responsible together for the ratiometric electrochemical analysis of ALP. PNP exhibits a straightforward current response toward ALP content; however, PO₄^3- cannot show a direct electrochemical signal thus is rationally designed to offer an alternative response by linking it with the specific CoOOH nanozyme-catalyzed reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂, in which the nanozyme-catalyzed product oxTMB shows a direct reduction current at the GCE, and significantly decreases with increasing PO₄^3- species due to the good inhibition of PO₄^3- toward CoOOH nanozyme activity. As a result, a ratiometric electrochemical strategy for ALP analysis with a low limit of detection of 0.366 U/L (S/N = 3) was successfully achieved by integrating the above direct and indirect dual electrochemical responses. This developed bioassay can allow the quantitative diagnosis of ALP activity especially with a label-free and modification-free merit, therefore paving the way for simple, convenient, and portable electroanalytical tools in biosensing design and application.