Biocompatible fluorescent probe for detecting mitochondrial alkaline phosphatase activity in live cells

Alkaline phosphatase (ALP) is an enzyme that actively plays a significant role in the various metabolic processes by transferring a phosphate group to the protein, nucleic acid, etc. The elevated level of ALP in blood plasma is the hallmark of inflammation/cancer. The hyperactive mitochondria in cancer cells produce an excess of ATP to fulfill the high energy demand. Thus, we have developed a fluorescent probe Mito-Phos for ALP, which can detect phosphatase expression in mitochondria in live cells. The probe Mito-Phos has shown ~15-fold fluorescence intensity increments at 450 nm in the presence of 500 ng/mL of ALP. It takes about 60 min to consume the whole amount of ALP (500 ng/mL) in physiological buffer saline. It can selectively react with ALP even in the presence of other probable cellular reactive components. It is highly biocompatible and nontoxic to the live cells. It has shown ALP expression in a dose-dependent manner by providing concomitant fluorescence images in the blue-channel region. It has localized exclusively in the mitochondria in live cells. The probe Mito-Phos is highly biocompatible with the ability to assess ALP expression in mitochondria in live cells.

Ratiometric sensing of alkaline phosphatase based on the catalytical activity from Mn-Fe layered double hydroxide nanosheets

Two-dimensional (2D) Mn-Fe layered double hydroxide (LDH) nanosheets are firstly examined to mediate an O-phenylenediamine (OPD) based fluorescent switch in the presence of ascorbic acid (AA). On one hand, Mn-Fe LDH mimicked the functions of oxidase to catalyze the oxidation of OPD to OPDox, emitting fluorescence at 565 nm. On the other hand, Mn-Fe LDH acts as a superior catalyst for the reaction between AA and OPD to generate 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (N-heterocyclic compound) with an emergence of the maximum emission at 425 nm (ca. 6 fold). The presence of AA not only induces the enhanced emission at 425 nm from the N-heterocyclic compound, but also leads to decreased fluorescence at 565 nm due to the decomposition of Mn-Fe LDH nanosheets. On the basis of the reversed fluorescence response at 425 and 565 nm, ratiometric fluorescence sensing methods (ΔF425 nm/ΔF565 nm) are developed for the determination of AA. With the assistance of alkaline phosphatase (ALP), the activity of ALP can be monitored using the ratiometric platform based on the hydrolyzing ascorbic acid 2-phosphate to yield AA with the detection limit of 0.16 mU mL-1. Different from the traditional ratiometric sensing platform, where two fluorescent probes are often introduced, the present ratiometric system derived from one signal precursor holds great potential in developing a facile platform and broadens the application of 2D nanomaterials in the field of biology.

Near-infrared ratiometric probe with a self-immolative spacer for rapid and sensitive detection of alkaline phosphatase activity and imaging in vivo

Alkaline phosphatase (ALP), an enzyme that catalyzes the hydrolysis of phosphate groups, is closely associated with many diseases, including bone disease, prostate cancer, and diabetes. Thus, new assays for ALP detection in live cells are needed to better understand its role in related biological processes. In this study, we constructed a novel near-infrared ratiometric fluorescent probe for detecting ALP activity with high sensitivity. The probe uses a new self-immolative mechanism that can achieve a rapid response (within 10 min) to ALP, detected as a spectral shift (from 580 to 650 nm). This method effectively avoids issues related to instrument variability, and the near-infrared fluorescence emission (650 nm) makes it more suitable for biological detection. Moreover, the high sensitivity (14-fold enhancement of the fluorescence ratio F₆₅₀/F₅₈₀) and low detection limit (0.89 U L^-1) for ALP allows the probe to be adapted to complex biological environments. The assay was successfully performed using serum samples with a linear range of ALP of up to 150 U L^-1. We used the developed probe to detect and image endogenous ALP in cells with satisfactory results, and we successfully used the probes to detect changes in endogenous ALP levels in zebrafish caused by drug-induced organ damage.