Self-Assembled Redox System for Bioelectrocatalytic Assay of L-Ascorbylphosphate and Alkaline Phosphatase Activity

Ratiometric fluorescence determination of alkaline phosphatase activity based on carbon dots and Ce3+-crosslinked copper nanoclusters

A new ratiometric fluorescent probe for efficient determination of ALP was developed. The probe was constructed by combining Ce3+-crosslinked copper nanoclusters (Ce3+-CuNCs) which exhibit the aggregation-induced emission (AIE) feature with carbon dots (CDs). The introduction of phosphate (Pi) induced the generation of CePO4 precipitation, resulting in significant decrease of fluorescence emission of CuNCs at 634 nm. At the same time, the fluorescence of CDs at 455 nm was obviously enhanced, thus generating ratiometric fluorescence response. Based on the fact that the hydrolysis of pyrophosphate (PPi) by ALP can produce Pi, the CD/Ce3+-CuNCs ratiometric probe was successfully used to determine ALP. A good linear relationship between the ratiometric value of F455/F634 and ALP concentrations ranging from 0.2 to 80 U·L- 1 was obtained, with a low detection limit of 0.1 U·L- 1. The ratiometric responses of the probe resulted in the visible fluorescence color change from orange red to blue with the increase of ALP concentration. The smartphone-based RGB recognition of the fluorescent sample images was used for ALP quantitative determination. A novel ratiometric fluorescent system based on Ce3+-CuNCs with AIE feature and CDs were constructed for efficient detection of ALP.

Selective Detection of Alkaline Phosphatase Activity in Environmental Water Samples by Copper Nanoclusters Doped Lanthanide Coordination Polymer Nanocomposites as the Ratiometric Fluorescent Probe

In this paper, a novel, accurate, sensitive and rapid ratiometric fluorescent sensor was fabricated using a copper nanoclusters@infinite coordination polymer (ICP), specifically, terbium ion-guanosine 5'-disodium (Cu NCs@Tb-GMP) nanocomposites as the ratiometric fluorescent probe, to detect alkaline phosphatase (ALP) in water. The fluorescence probe was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The experimental results showed that, compared with Tb-GMP fluorescent sensors, Cu ratiometric fluorescent sensors based on NCs encapsulated in Tb-GMP had fewer experimental errors and fewer false-positive signals and were more conducive to the sensitive and accurate detection of ALP. In addition, the developed fluorescent probe had good fluorescence intensity, selectivity, repeatability and stability. Under optimized conditions, the ratiometric fluorescent sensor detected ALP in the range of 0.002-2 U mL^-1 (R² = 0.9950) with a limit of detection of 0.002 U mL^-1, and the recovery of ALP from water samples was less than 108.2%. These satisfying results proved that the ratiometric fluorescent probe has good application prospects and provides a new method for the detection of ALP in real water samples.

A simple enzyme-catalyzed reaction induced "switch" type fluorescence biosensor based on carbon nitride nanosheets for the assay of alkaline phosphatase activity

An enzyme-catalyzed fluorescence "switch" type sensor was constructed for the determination of alkaline phosphatase (ALP) activity by combining the fluorescence quenching effect of Ag+ on ultrathin g-C3N4 nanosheets (CNNSs) with the simple redox reaction of AA and Ag+. Briefly, Ag+ exhibits a significant quenching effect on the fluorescence of CNNSs. Thus the fluorescence signal of the CNNS-Ag+ system is extremely weak even in the presence of l-ascorbic acid-2-phosphate (AAP) ("off" state). When ALP coexists in the system, the enzyme can specifically catalyze the hydrolysis of AAP to form ascorbic acid (AA), which reduces Ag+ to Ag0. In this case, the fluorescence signal of the system is recovered ("on" state). Based on this principle, a signal-enhanced CNNS fluorescence sensor was developed to determine the activity of alkaline phosphatase. The experimental results show that the detection range of alkaline phosphatase is 0.5-20 U L-1, and the detection limit is 0.05 U L-1 (S/N = 3). Meanwhile, this method was used to assay ALP in serum samples.

A carbon dot doped lanthanide coordination polymer nanocomposite as the ratiometric fluorescent probe for the sensitive detection of alkaline phosphatase activity

The development of sensitive methods for alkaline phosphatase (ALP) activity analysis is an important analytical topic. Based on the stimulus-responsive lanthanide coordination polymer, a simple ratiometric fluorescence sensing strategy was proposed to detect ALP activity. A carbon dot (CD) doped fluorescent supramolecular lanthanide coordination polymer (CDs@Tb-GMP) was prepared with Tb³⁺ and the ligand guanine single nucleotide (GMP). To construct a ratiometric fluorescence biosensor, the fluorescence of Tb-GMP was used as a response signal, and the fluorescence of CDs was used as a reference signal due to its good stability. When excited at 290 nm, the polymer network Tb-GMP emits characteristic fluorescence at 545 nm, while the CDs encapsulated in the polymer network emit fluorescence at 370 nm. After adding ALP to the system, the substrate GMP can be hydrolyzed by ALP, resulting in the destruction of the polymer network. Accordingly, the fluorescence of Tb-GMP significantly decreased, while the fluorescence of CDs slightly increased due to their release from the polymer network. By comparing the relationship between the fluorescence intensity ratio of the two signals and the concentration of ALP, sensitive detection of ALP could be achieved with the linear range from 0.5 to 80 U L^-1 and a detection limit of 0.13 U L^-1. Furthermore, the proposed ratiometric sensing system was applied to the detection of ALP in human serum samples with desirable results, indicating potential application in clinical diagnosis.

Steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer and pyrene for alkaline phosphatase fluorescent sensing

We herein report a strategy for sensitive alkaline phosphatase (ALP) fluorescent sensing based on steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer (polyβ-CD) and pyrene. The fluorescence of pyrene was enhanced more than 10 times through supramolecular assembly with polyβ-CD. The 5'-phosphorylated dsDNA probe with pyrene attached on the 3'-terminal could be cleaved by λ exonuclease (λ exo), yielding pyrene attached on mononucleotides. Pyrene attached on mononucleotides could easily enter the cavity of polyβ-CD, resulting in fluorescence enhancement. When ALP was introduced, it could remove 5'-phosphate groups from dsDNA and then prevented the cleavage of dsDNA. Pyrene attached on dsDNA was difficult to enter the cavity of polyβ-CD because of steric hindrance, resulting in an inconspicuous fluorescence enhancement. Owing to the excellent fluorescence enhancement during steric hindrance regulated supramolecular assembly, excellent performance of the assay method was achieved for ALP with a detection limit of 0.04 Um L(-1). The detection limit was superior or comparable with the reported methods. Besides, this method was simple in design, avoiding double-labeling of probe.

A highly sensitive homogeneous electrochemical assay for alkaline phosphatase activity based on single molecular beacon-initiated T7 exonuclease-mediated signal amplification

A highly sensitive homogeneous electrochemical assay for alkaline phosphatase activity based on single molecular beacon-initiated T7 exonuclease-assisted signal amplification.

A new fluorometric turn-on assay for alkaline phosphatase and inhibitor screening based on aggregation and deaggregation of tetraphenylethylene molecules

Based on the consideration that compound 1 with a -PO3H2 group can be hydrolyzed into compound 3 which shows low solubility in aqueous solutions and thus aggregation can occur easily, a new fluorescence turn-on assay has been constructed for alkaline phosphatase (ALP) with compound 1. ALP at concentrations as low as 18 mU mL(-1) can be assayed with compound 1. Moreover, compound 1 has been successfully applied for ALP assay in living cells. Also, compound 1 is useful for screening inhibitors of ALP.