Simultaneous detection of alkaline phosphatase and β-galactosidase activity using SERRS

In situ formation of fluorescence species for the detection of alkaline phosphatase and organophosphorus pesticide via the ascorbate oxidase mimetic activity of AgPd bimetallic nanoflowers

Sensitive detection strategies for enzymes and their inhibitors not only have critical significance in clinical diagnosis but can be extended to food and environment analysis. Here, bimetallic AgPd alloy nanoflowers were synthesized using carbon dots as the reductant via a two-step reduction method. The AgPd bimetallic nanoflowers exhibit ascorbate oxidase mimetic activity, which can rapidly catalyze the oxidization of ascorbic acid to dehydroascorbic acid (DHA). The DHA can then react with o-phenylenediamine (OPD) to produce 3-(1, 2-dihydroxyethyl)furo[3,4-b] quinoxalin-1(3H)-one (DFQ), accompanying with the characteristic fluorescence peak at 440 nm for DFQ. Alkaline phosphatase catalyzes l-ascorbyl-2-phosphate to generate AA, while organic phosphorus pesticides (OPPs) such as chlorpyrifos can inhibit the activity of alkaline phosphatase. By utilizing the enzyme-nanozyme tandem catalytic reaction, the fluorescence of the system varies in the presence of different concentrations of ALP or OPPs, which can be used to detect ALP in serum and OPPs in vegetables and fruits.

Controllable sensitization of Zr-MOFs by using CdS and its application for photoelectrochemical detection of alkaline phosphatase

CdS quantum dots (QDs) are attached onto zirconium-based metal-organic frameworks (Zr-MOFs) with DNA as a bridge to boost the photoelectrochemical (PEC) activity of Zr-MOFs, and the sensitization of Zr-MOFs by using CdS QDs is regulated by the alkaline phosphatase (ALP)-catalyzed hydrolysis of tripolyphosphate, enabling sensitive "signal-on" PEC detection of ALP activity.

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.

Raman Scattering-Based Biosensing: New Prospects and Opportunities

The growing interest in the development of new platforms for the application of Raman spectroscopy techniques in biosensor technologies is driven by the potential of these techniques in identifying chemical compounds, as well as structural and functional features of biomolecules. The effect of Raman scattering is a result of inelastic light scattering processes, which lead to the emission of scattered light with a different frequency associated with molecular vibrations of the identified molecule. Spontaneous Raman scattering is usually weak, resulting in complexities with the separation of weak inelastically scattered light and intense Rayleigh scattering. These limitations have led to the development of various techniques for enhancing Raman scattering, including resonance Raman spectroscopy (RRS) and nonlinear Raman spectroscopy (coherent anti-Stokes Raman spectroscopy and stimulated Raman spectroscopy). Furthermore, the discovery of the phenomenon of enhanced Raman scattering near metallic nanostructures gave impetus to the development of the surface-enhanced Raman spectroscopy (SERS) as well as its combination with resonance Raman spectroscopy and nonlinear Raman spectroscopic techniques. The combination of nonlinear and resonant optical effects with metal substrates or nanoparticles can be used to increase speed, spatial resolution, and signal amplification in Raman spectroscopy, making these techniques promising for the analysis and characterization of biological samples. This review provides the main provisions of the listed Raman techniques and the advantages and limitations present when applied to life sciences research. The recent advances in SERS and SERS-combined techniques are summarized, such as SERRS, SE-CARS, and SE-SRS for bioimaging and the biosensing of molecules, which form the basis for potential future applications of these techniques in biosensor technology. In addition, an overview is given of the main tools for success in the development of biosensors based on Raman spectroscopy techniques, which can be achieved by choosing one or a combination of the following approaches: (i) fabrication of a reproducible SERS substrate, (ii) synthesis of the SERS nanotag, and (iii) implementation of new platforms for on-site testing.

Multicolor diagnosis of salivary alkaline phosphatase triggered by silver-coated gold nanobipyramids

Alkaline phosphatase (ALP) is one of the most versatile biomarkers for early detection of several diseases, such as oral carcinomas and periodontitis; therefore, great efforts have been dedicated for developing an ALP biosensor. Multicolor detection of ALP in saliva is ideal for a point-of-care diagnosis; however, this approach is very challenging since spectral responses over wavelengths of several tens of nanometers have thus far remained difficult to achieve. In this work, a colorimetric biosensor for ALP assay has been developed based on ALP affinity to dephosphorylate glucose phosphate into glucose, which has the affinity to deposit Ag nanoshells onto Au nanobipyramids with a multicolor response. This approach provides a blue shift of localized surface plasmon resonance (LSPR) as large as 190 nm corresponding to distinctive color changes, from yellowish brown to red based on the thickness of the formed Ag shell around the Au nanobipyramids. The change in the LSPR has been conducted for highly sensitive quantitative bioassay of ALP with a detectable multicolor change with linear dynamic range of 0.1-20 U/L and low limit of detection (LOD) of 0.085 U/L. Furthermore, the developed multicolor ALP biosensor exhibits high selectivity with high recovery of 98.6% demonstrating  its reliability and suitability for a point-of-care diagnosis.

Nano-octahedral bimetallic Fe/Eu-MOF preparation and dual model sensing of serum alkaline phosphatase (ALP) based on its peroxidase-like property and fluorescence

Herein a nano-scale bimetallic Fe/Eu-MOF with a regular octahedral structure was synthesized for the first time. The synthesized Fe/Eu-MOF has both peroxidase-like activity and fluorescence properties. Fe/Eu-MOF can catalyze H₂O₂ to oxidize the chromogenic substrate TMB to produce blue oxTMB, which has ultraviolet absorption at 652 nm. Unexpectedly, the generated oxTMB can effectively quench the fluorescence of the catalyst Fe/Eu-MOF at 450 nm. The quenching mechanism is mainly the internal filtration effect (IFE), accompanied by static quenching (SQE), Förster resonance energy transfer (FRET) and photoelectron transfer (PET). Fe/Eu-MOF has a high affinity for sodium pyrophosphate (PPi). PPi can be adsorbed to the surface of Fe/Eu-MOF, destroying the structure of Fe/Eu-MOF and inhibiting its catalytic activity, resulting in a decrease in UV absorbance and the decline of fluorescence quenching. In contrast, phosphoric acid (Pi) has almost no effect on the reaction system. Alkaline phosphatase (ALP) can catalyze the hydrolysis of PPi to Pi, thereby reducing the inhibitory effect of PPi. Based on this, we successfully constructed a dual-mode ALP sensor with high selectivity. The linear ranges based on the 652 nm absorption or the fluorescence detection are from 1 to 200 U/L, and the detection limits are 0.6 for the absorption method and 0.9 U/L for the fluorescence method, respectively.

A colorimetric alkaline phosphatase biosensor based on p-aminophenol-mediated growth of silver nanoparticles

Alkaline phosphatase (ALP) is an enzyme that catalyzes the dephosphorylation of proteins, nucleic acids, and biomolecules. It is a potential biomarker for diverse diseases such as breast cancer, osteopenia, and hepatobiliary. Herein, we developed a colorimetric sensor for the ALP assay based on its enzymatic activity to dephosphorylate the p-aminophenol phosphate (pAPP) into pAP. In a solution containing silver nanoparticles (AgNPs) and Ag⁺ ions prepared using a low concentration of NaBH₄, pAP mediates the growth of AgNPs by reducing the concentration of Ag⁺ ions to enhance the intensity of localized surface plasmon resonance as the pAPP cannot induce a reduction of the remaining Ag⁺ due to the masking of the hydroxyl with phosphate. The quantitative assay of the ALP was demonstrated via the colorimetric detection of the pAP-mediated growth of AgNPs in the presence of an ALP. The highly sensitive enzymatic growth of AgNPs provided a wider dynamic linear range of 0.5-225 U/L with a lower limit of detection of 0.24 U/L than that previously reported. The use of pAP resulted in excellent selectivity of the sensor for the ALP assay in human serum, yielding a high recovery rate and a high precision of 99.2 ± 1.5 % for the standard addition method.

A two fluorescent signal indicator-based ratio fluorometric alkaline phosphatase assay based on one signal precursor

Two fluorescent signal indicators were simply converted from one organic precursor system by using the superior oxidation capability of manganese dioxide (MnO2) nanosheets for the first time, finally resulting in the successful fabrication of a ratio fluorometric bioassay of alkaline phosphatase (ALP).

Target-induced transcription amplification to trigger the trans-cleavage activity of CRISPR/Cas13a (TITAC-Cas) for detection of alkaline phosphatase

Herein, an ultra-sensitive alkaline phosphatase (ALP) sensing strategy is developed by target-induced transcription amplification to trigger the trans-cleavage activity of Cas13a (TITAC-Cas). A double-stranded DNA duplex integrating a T7 promoter with 5'-phosphate and a transcription template (5'P-dsDNA) serves as the ALP substrate. In the absence of ALP, 5'P-dsDNA can be degraded by the λexo, leading to the subsequent transcription failure. In the presence of ALP, dephosphorylation reaction converts the 5'P-dsDNA to 5'OH-dsDNA and provides the protection for T7 promoter against the λexo-digestion. The intact T7 promoter of 5'OH-dsDNA can activate T7 transcription to produce a mass of single-stranded RNA (ssRNA). The ssRNA products possess a full complementarity to the spacer of crRNA and activate the ssRNase activity of CRISPR/Cas13a. As a result, Cas13a exhibits the indiscriminate cleavage of collateral FQ-reporter to release significant fluorescence signal, realizing the ultra-sensitive detection of ALP. Due to the triple signal amplification (ALP self-catalysis, T7 transcription amplification, and trans-cleavage of CRISPR/Cas13a), TITAC-Cas assay shows the ultra-sensitive detection of ALP activity with a wide linear range from 0.008 to 250 U∙L^-1). The LOD is calculated to be 6 ± 0.52 mU∙L^-1. TITAC-Cas assay is also successfully applied for analysis of ALP activity in HepG2 cell lysate with high fidelity. In addition, this method is employed to screen ALP inhibitor.

A turn-on near-infrared fluorescent probe for visualization of endogenous alkaline phosphatase activity in living cells and zebrafish

Alkaline phosphatase (ALP) is an essential hydrolase and widely distributed in living organisms. It plays important roles in various physiological and pathological processes. Herein, a turn-on near-infrared (NIR) fluorescent probe (DXMP) was developed for sensitive detection of ALP activity both in vitro and in vivo based on the intramolecular charge transfer (ICT) mechanism. Upon incubation with ALP, DXMP exhibited a strong fluorescence increment at 640 nm, which was attributed to the fact that ALP-catalyzed cleavage of the phosphate group in DXMP induced the transformation of DXMP into DXM-OH. The probe exhibited prominent features including outstanding selectivity, high sensitivity, and excellent biocompatibility. More importantly, it has been successfully used to detect and image endogenous ALP in living cells and zebrafish.

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.

A light-up near-infrared probe with aggregation-induced emission characteristics for highly sensitive detection of alkaline phosphatase

Developing activatable near-infrared (NIR) probes to specifically monitor and visualize the activities of cancer-related enzymes is highly significant yet challenging in early cancer diagnosis. Taking advantage of the unique photophysical characteristics of aggregation-induced emission (AIE) fluorophores, here we design and synthesize a novel activatable probe QMTP by conjugating an AIE fluorophore quinolone-malononitrile to a hydrophilic phosphate-modified phenol group. The probe was initially non-fluorescent in aqueous solution due to its good water solubility, but was readily activated to generate a strong NIR fluorescence upon treatment with alkaline phosphatase (ALP), which enables specific detection of ALP activity. Furthermore, we have employed QMTP to monitor and spatially map the activity of endogenous ALP both in cancer cells and in drug-treated zebrafish larvae. The experimental results reveal that the QMTP probe has great specificity and sensitivity for ALP detection. We thus believe that our work offers a promising tool for accurate detection of ALP-associated diseases in preclinical applications.

An ALP-activatable and mitochondria-targeted probe for prostate cancer-specific bimodal imaging and aggregation-enhanced photothermal therapy

Tumor-derived alkaline phosphatase (ALP) is over-expressed in metastatic prostate cancer. The development of selective probes for ALP detection is therefore critical for early diagnosis and therapy of metastatic prostate cancer. Herein, we develop a mitochondria-targeted near-infrared activatable fluorescent/photoacoustic (NIR FL/PA) probe for the selective detection of prostate cancer-derived ALP and aggregation-enhanced photothermal therapy. Upon dephosphorylation, the probes are activated and they provide a red-shifted strong absorption and emission in the NIR window and thus enable NIR FL and PA imaging of ALP activity in tumor tissues. Particularly, the activated probes self-assemble in situ into a supramolecular network structure which induces cell apoptosis and significantly enhances the photothermal therapy efficacy.

Ratiometric fluorescent sensor for visual determination of copper ions and alkaline phosphatase based on carbon quantum dots and gold nanoclusters

In this work, a novel ratiometric fluorescent sensor, based on carbon dots (CDs) and gold nanoclusters (AuNCs), is developed for highly sensitive and selective visual colorimetric detection of Cu²⁺ and alkaline phosphatase (ALP). The ratiometric fluorescent sensor was synthesized by covalently linking 11-mercaptoundecanoic acid (11-MUA)-stabilized AuNCs to the surface of amino-functionalized CD/SiO₂ nanoparticles. The red fluorescence of the AuNCs can be quenched by Cu²⁺ owing to coordination between Cu²⁺ and 11-MUA; however, the blue emission of the CDs was insensitive to Cu²⁺ owing to the protective silica shell. The quenching of the AuNCs' fluorescence returned when PPi was added because of the higher affinity between Cu²⁺ and PPi than that between Cu²⁺ and 11-MUA. In the presence of ALP, PPi was catalytically hydrolyzed into phosphate (Pi), which showed a much weaker affinity for Cu²⁺. Thus, Cu²⁺ ions were released, and the fluorescence of the AuNCs was quenched once more. Based on this principle, Cu²⁺ and ALP could be simultaneously detected. The developed ratiometric fluorescent sensor could detect Cu²⁺ over a range from 0.025 to 4 μM with a detection limit of 0.013 μM and ALP over a range from 0.12 to 15 U/L with a detection limit of 0.05 U/L. The present method was successfully applied for the detection of Cu²⁺ and ALP in real water samples and in human serum samples, respectively. This ratiometric fluorescent approach may provide a highly sensitive and accurate platform for visual Cu²⁺ and ALP sensing in environmental monitoring and medical diagnosis.

Near-infrared mito-specific fluorescent probe for ratiometric detection and imaging of alkaline phosphatase activity with high sensitivity

A NIR ratiometric fluorescent probe based on cyanine dye was developed for detecting and intracellular imaging of ALP activity with high sensitivity.

Alkaline phosphatase labeled SERS active sandwich immunoassay for detection of Escherichia coli

In this study, a sandwich immunoassay method utilizing enzymatic activity of alkaline phosphatase (ALP) on 5-bromo-4-chloro-3-indolyl phosphate (BCIP) for Escherichia coli (E. coli) detection was developed using surface enhanced Raman spectroscopy (SERS). For this purpose, spherical magnetic gold coated core-shell nanoparticles (MNPs-Au) and rod shape gold nanoparticles (Au-NRs) were synthesized and modified for immunomagnetic separation (IMS) of E. coli from the solution. In order to specify the developed method to ALP activity, Au-NRs were labeled with this enzyme. After successful construction of the immunoassay, BCIP substrate was added to produce the SERS-active product; 5-bromo-4-chloro-3-indole (BCI). A good linearity (R²=0.992) was established between the specific SERS intensity of BCI at 600cm^-1 and logarithmic E. coli concentration in the range of 1.7×10¹-1.7×10⁶cfumL^-1. LOD and LOQ values were also calculated and found to be 10cfumL^-1 and 30cfumL^-1, respectively.

FRET Effect between Fluorescent Polydopamine Nanoparticles and MnO2 Nanosheets and Its Application for Sensitive Sensing of Alkaline Phosphatase

As an essential and universal hydrolase, alkaline phosphatase (ALP) has been identified as a crucial indicator of various diseases. Herein, we, for the first time, expanded the application of fluorescent polydopamine (F-PDA) nanoparticles to nanoquencher-based biosensing system, as well as discovered the reversible quenching effect of manganese dioxide (MnO₂) nanosheets on the fluorescence of F-PDA nanoparticles and intensively confirmed the quenching mechanism of Förster resonance energy transfer by using transmission electron microscopy, UV-vis, Fourier transform infrared spectroscopy, and fluorescence lifetime experiments. By means of the ALP-triggered generation of ascorbic acid (AA) from the substrate ascorbic acid 2-phosphate, the AA-triggered reduction of MnO₂ nanosheets to Mn²⁺, as well as the clear quenching mechanism of F-PDA nanoparticles by MnO₂ nanosheets, we have developed a label-free, low-cost, visual, and facile synthetic fluorescent biosensor for convenient assay of ALP activity. The fluorescent bioassay shows a good linear relationship from 1 to 80 mU/mL (R² = 0.999), with a low detection limit of 0.34 mU/mL, and the excellent applicability in human serum samples demonstrates potential applications in clinical diagnosis and biomedical research.

Determination of the activity of alkaline phosphatase by using nanoclusters composed of flower-like cobalt oxyhydroxide and copper nanoclusters as fluorescent probes

The authors describe a sensitive fluorometric method for the determination of the activity of alkaline phosphatase (ALP). It is based on the use of a composite prepared consisting of flower-like cobalt oxyhydroxide (CoOOH) and copper nanoclusters (CuNCs). On formation of the CuNC-CoOOH aggregates, the fluorescence of the CuNCs is quenched by the CoOOH sheets. If, however, the CoOOH sheets are reduced to Co(II) ions in the presence of ascorbic acid (AA), fluorescence recovers. AA is formed in-situ by hydrolysis of the substrate ascorbic acid 2-phosphate (AA2P) as catalyzed by ALP. Thus, the ALP activity can be detected indirectly by kinetic monitoring of the increase in fluorescence, best at excitation/emission wavelengths of 335/410 nm. The assay allows ALP to be determined in 0.5 to 150 mU·mL^-1 activity range and with a 0.1 mU·mL^-1 detection limit. The method was successfully applied to the determination of ALP activity in (spiked) human serum samples. The assay has attractive features in being of the off-on type and immune against false positive results. Graphical Abstract A fluorescent bioassay is reported for the determination of the activity of alkaline phosphatase (ALP). It is exploiting the ascorbic acid (AA)-induced decomposition of nanoclusters composed of flower-like cobalt oxyhydroxide and copper nanoclusters. ALP catalyzes hydrolysis of ascorbic acid 2-phosphate (AA2P) and dephosphorylation to form AA.

An impedimetric determination of alkaline phosphatase activity based on the oxidation reaction mediated by Cu2+ bound to poly-thymine DNA

A novel impedimetric assay for the accurate determination of alkaline phosphatase (ALP) activity is developed based on the Cu²⁺-mediated oxidation of ascorbic acid on a poly-thymine DNA-modified electrode.

Molybdenum oxide quantum dots prepared via a one-step stirring strategy and their application as fluorescent probes for pyrophosphate sensing and efficient antibacterial materials

MoO_x QDs were prepared using a one-step stirring treatment of MoO₃ powder in DMSO. They can be used as efficient fluorescent probes and antibacterial materials.

Inner filter effect based fluorometric determination of the activity of alkaline phosphatase by using carbon dots codoped with boron and nitrogen

Boron and nitrogen codoped carbon dots functionalized with cyclodextrin (β-CD-N/B-C-dots) were obtained from β-cyclodextrin. The material displays strong fluorescence (with excitation/emission peak wavelengths of 400/500 nm) and was characterized by UV-vis, transmission electron microscopy and FTIR. If the substrate p-nitrophenylphosphate is enzymatically cleaved by alkaline phosphatase (ALP), a yellow product is formed whose absorption overlaps the excitation spectrum of the β-CD-N/B-C-dots. Hence, fluorescence is reduced due to an inner filter effect. In additon, the β-CD cavity offers a pocket for substrate recognition. The findings were used to design a method for the determination of the activity of ALP. It has a working range that extends from 0.003 to 5.5 U·L^-1, with a 0.3 mU·L^-1 detection limit. The method is fast, simple, inexpensive, and highly sensitive and selective. Graphical abstract Schematic of an inner filter effect based probe for alkaline phosphatase based on the use boron and nitrogen co-doped carbon dots (N/B-C-dots) modified with β-cyclodextrin (β-CD). PNPP: p-Nitrophenylphosphate; PNP: p-Nitrophenol anion.

Reaction-Based Off-On Near-infrared Fluorescent Probe for Imaging Alkaline Phosphatase Activity in Living Cells and Mice

Alkaline phosphatases are a group of enzymes that play important roles in regulating diverse cellular functions and disease pathogenesis. Hence, developing fluorescent probes for in vivo detection of alkaline phosphatase activity is highly desirable for studying the dynamic phosphorylation in living organisms. Here, we developed the very first reaction-based near-infrared (NIR) probe (DHXP) for sensitive detection of alkaline phosphatase activity both in vitro and in vivo. Our studies demonstrated that the probe displayed an up to 66-fold fluorescence increment upon incubation with alkaline phosphatases, and the detection limit of our probe was determined to be 0.07 U/L, which is lower than that of most of alkaline phosphatase probes reported in literature. Furthermore, we demonstrated that the probe can be applied to detecting alkaline phosphatase activity in cells and mice. In addition, our probe possesses excellent biocompatibility and rapid cell-internalization ability. In light of these prominent properties, we envision that DHXP will add useful tools for investigating alkaline phosphatase activity in biomedical research.

Metal-to-ligand charge-transfer: Applications to visual detection of β-galactosidase activity and sandwich immunoassay

In this work, we report a novel use of the distinctive metal-to-ligand charge-transfer (MLCT) absorption properties of the chromogenic Fe(BPDS)₃^4- (BPDS=bathophenanthroline disulfonic acid) reporter for the visual detection of β-galactosidase (β-Gal) activity and sandwich immunoassay. The enzymatic hydrolysis of the substrate p-aminophenyl-β-D-galactopyranoside can switch on the reduction of Fe³⁺ to Fe²⁺ and the subsequent complexation of Fe²⁺ with the BPDS ligand to generate the Fe(BPDS)₃^4- reporter, leading to the appearance of the intense MLCT absorption band at 535nm and the colorless-to-red color change of the solution. Simply through a single step, the activity of β-Gal can be sensitively and selectively detected within the dynamic range of 0-220mUmL^-1, with a limit of detection (LOD) of 1.69mUmL^-1. This approach is applicable for the visual detection of β-Gal activities in the presence of complex human serum samples. Besides, when integrated with the sandwich immunoassay of carcinoembryonic antigen, a LOD of 1.16ngmL^-1 can be achieved. In light of its prominent simplicity and practicality, our MLCT-based approach holds great potential in diagnostic and analytical applications.

A Turn-On Fluorescent Sensor for Selective and Sensitive Detection of Alkaline Phosphatase Activity with Gold Nanoclusters Based on Inner Filter Effect

In this work, a novel approach for simple and sensitive determination of alkaline phosphatase (ALP) is developed on the basis of an inner filter effect of p-nitrophenylphosphate (PNPP) on the fluorescence of gold nanoclusters (AuNCs). AuNCs with a high quantum yield of 12% were synthesized by one-pot strategy and were directly applied as fluorescent substance. When AuNCs were mixed with PNPP, the fluorescence of the AuNCs was remarkably quenched or was decreased via the inner filter effect since the absorption spectrum of PNPP overlaps well with the excitation spectrum of the AuNCs. While in the presence of ALP, PNPP was catalytically hydrolyzed into p-nitrophenol, which has different absorption characteristics from those of PNPP, resulting in the recovery of the AuNCs fluorescence. Thus, a novel "turn-on" fluorescent sensor for detecting ALP was established with a detection limit as low as 0.002 U/L (signal-to-noise ratio of 3). The turn-on fluorescent sensor exhibits many merits such as high sensitivity, excellent selectivity, and high signal output because of the low background signals. In addition, the developed sensing method was successfully applied to investigate ALP inhibitors and ALP determination in serum samples. A good linear relationship was obtained in the range from 0.02 to 50 U/L, and satisfactory recoveries at four spiking levels of ALP ranged from 95% to 106% with precision below 5%. The very simple sensing approach proposed here should promote the development of fluorescence turn-on chemosensors for chemo/biodetection.

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.

Naked-eye sensitive detection of alkaline phosphatase (ALP) and pyrophosphate (PPi) based on a horseradish peroxidase catalytic colorimetric system with Cu(ii)

In this paper, a novel colorimetric method for the detection of alkaline phosphatase (ALP) and pyrophosphate (PPi) was designed based on a Cu²⁺–horseradish peroxidase (HRP)–3,3′,5,5′-tetra-methylbenzidine (TMB)–H₂O₂ system.

Multiplex in vitro detection using SERS

This review focuses on the recent advances in SERS and its potential to detect multiple biomolecules in clinical samples.

Recent advances in the development of synthetic chemical probes for glycosidase enzymes

The emergence of synthetic glycoconjugates as chemical probes for the detection of glycosidase enzymes has resulted in the development of a range of useful chemical tools with applications in glycobiology, biotechnology, medical and industrial research. Critical to the function of these probes is the preparation of substrates containing a glycosidic linkage that when activated by a specific enzyme or group of enzymes, irreversibly releases a reporter molecule that can be detected. Starting from the earliest examples of colourimetric probes, increasingly sensitive and sophisticated substrates have been reported. In this review we present an overview of the recent advances in this field, covering an array of strategies including chromogenic and fluorogenic substrates, lanthanide complexes, gels and nanoparticles. The applications of these substrates for the detection of various glycosidases and the scope and limitations for each approach are discussed.

Carbon quantum dots-based recyclable real-time fluorescence assay for alkaline phosphatase with adenosine triphosphate as substrate

A convenient, reliable, and highly sensitive real-time assay for alkaline phosphatase (ALP) activity in the continuous and recyclable way is established on the basis of aggregation and disaggregation of carbon quantum dots (CQDs) through the competitive assay approach. CQDs and adenosine triphosphate (ATP) were used as the fluorescent indicator and substrate for ALP activity assessment, respectively. Richness of carboxyl groups on the surface of CQDs enables their severe aggregation triggered by cerium ions, which results in effective fluorescence quenching. Under the catalytic hydrolysis of ALP, ATP can be rapidly transformed to phosphate ions. Stronger affinity of phosphate ions to cerium ions than carboxyl groups is taken advantage of to achieve fluorescence recovery induced by redispersion of CQDs in the presence of ALP and ATP. Quantitative evaluation of ALP activity in a broad range from 4.6 to 383.3 U/L with the detection limit of 1.4 U/L can be realized in this way, which endows the assay with high enough sensitivity for practical detection in human serum. The assay can be used in a recyclable way for more than three times since the generated product CePO4 as a precipitate can be easily removed from the standard assay system. This strategy broadens the sensing application of fluorescent CQDs with excellent biocompatibility and provides an example based on disaggregation in optical probe development.