Copper sulfide nanoparticle-decorated graphene as a catalytic amplification platform for electrochemical detection of alkaline phosphatase activity

Facile Synthesis of Needle-like Copper Sulfide Structures as an Effective Electrochemical Sensor Material for Neurotransmitter Detection in Biological Samples

Electrochemical sensors, due to their excellent and unique features, are of high interest nowadays for the detection and monitoring of several biological compounds. In such a case, serotonin (SRN), an important neurotransmitter, was herein studied for its detection in biological fluids since its presence is more crucial to be monitored and detected in clinical and medical applications. Several study strategies have been used to determine the chemical and physical properties. The crystalline size of the constructed copper sulfide (Cu2S) material was measured to be 25.92 nm. The Cu2S was fabricated over the working surface and further analyzed for several sensor parameters to be optimized. The charge transfer resistance of the copper sulfide-modified glassy carbon electrode (Cu2S/GCE) was determined to be about 277.0 Ω. With the linear range from about 0.029 μM to 607.6 μM for SRN, the limit of detection (LOD) was calculated as 3.2 nM, with a good sensitivity of 13.23 μA μM-1 cm2. The sensor experienced excellent repeatability, reproducibility, and long-term stability. The fabricated electrode was selective with the presence of different interfering compounds. The real sample analysis, as determined with the regular addition method with human serum and urine samples, revealed a good recovery percentage. Thus, the employed fabricated electrode material will be highly effective in sensing other analytes of choice.

Fluorescence Turn-on Detection of Alkaline Phosphatase Activity and Al3+ Using Vitamin B6 Cofactor Conjugated GSH Capped Mn-doped ZnS Quantum Dots

The glutathione (GSH) functionalized Mn-doped ZnS quantum dots (GSH_Mn_ZnS QDs) was conjugated with pyridoxal 5'-phosphate (PLP). The -CHO group of vitamin B₆ cofactor PLP interacted with the -NH₂ group of GSH functionalized Mn_ZnS QDs. The conjugation of PLP quenched the fluorescence emission of GSH_Mn_ZnS QDs at 601 nm. Addition of alkaline phosphatase (ALP) catalytically dephosphorylated the PLP into pyridoxal that restored the fluorescence emission of GSH_Mn_ZnS QDs. With a sensitivity of 0.035 U/L, the PLP conjugated GSH_Mn_ZnS QDs was applied to quantify ALP activity in human serum and plasma. Further, the developed nanoprobe PLP conjugated GSH_Mn_ZnS QDs was also applied to detect Al³⁺. The complexation-induced fluorescence enhancement was observed at 492 nm upon the interaction of Al³⁺ with the PLP conjugated GSH_Mn_ZnS QDs. Without any interference from other tested metal ions, this nanoprobe can be employed to detect Al³⁺ down to 2.30 µM.

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.

Microwave-Assisted Synthesis of Sulfur Quantum Dots for Detection of Alkaline Phosphatase Activity

Sulfur quantum dots (SQDs) are a kind of pure elemental quantum dots, which are considered as potential green nanomaterials because they do not contain heavy metal elements and are friendly to biology and environment. In this paper, SQDs with size around 2 nm were synthesized by a microwave-assisted method using sulfur powder as precursor. The SQDs had the highest emission under the excitation of 380 nm and emit blue fluorescence at 470 nm. In addition, the SQDs had good water solubility and stability. Based on the synthesized SQDs, a fluorescence assay for detection of alkaline phosphatase (ALP) was reported. The fluorescence of the SQDs was initially quenched by Cr (VI). In the presence of ALP, ALP-catalyzed hydrolysis of 2-phospho-L-ascorbic acid to generate ascorbic acid. The generated ascorbic acid can reduce Cr (VI) to Cr (III), thus the fluorescence intensity of SQDs was restored. The assay has good sensitivity and selectivity and was applied to the detection of ALP in serum samples. The interesting properties of SQDs can find a wide range of applications in different sensing and imaging areas.

Detection of Pyrophosphate and Alkaline Phosphatase Activity Based on PolyT Single Stranded DNA - Copper Nanoclusters

The determination of pyrophosphate and alkaline phosphatase activity plays a significant role in medical diagnosis. In this work, a label-free "ON-OFF-ON" fluorescence strategy is developed for the analysis of pyrophosphate and alkaline phosphatase activity. Using PolyT single strand DNA as templates to synthesize fluorescent copper nanoparticles, the coordination effect of pyrophosphoric acid on Cu²⁺ inhibited the generation of fluorescence. Afterwards, the addition of alkaline phosphatase into hydrolyze pyrophosphoric acid resulted in the release of Cu^2+, whereby the fluorescence intensity could be recovered. Thereupon enhanced-sensitivity for alkaline phosphatase was obtained (0.1 mU/L), much better than previously reported methods. Meanwhile, it could be performed directly in homogeneous solution, which was very close to the actual activity level of alkaline phosphatase under physiological conditions. Likewise, satisfactory results were also obtained in specificity assessment, which demonstrated its potential application in clinical diagnosis. Notably, a new, sensitive, low-cost, short-time, and high-sensitivity platform for alkaline phosphatase detection was constructed, and the design of biosensor using DNA-templated Copper nanoclusters (CuNCs) was instructed in this study.

Alkaline Phosphatase Electrochemical Micro-Sensor Based on 3D Graphene Networks for the Monitoring of Osteoblast Activity

Alkaline phosphatase (ALP) is a significant biomarker that indicates osteoblast activity and skeletal growth. Efficient ALP detection methods are essential in drug development and clinical diagnosis. In this work, we developed an in-situ synthesized three-dimensional graphene networks (3DGNs)-based electrochemical sensor to determine ALP activity. The sensor employs an ALP enzymatic conversion of non-electroactive substrate to electroactive product and presents the ALP activity as an electrochemical signal. With 3DGNs as the catalyst and signal amplifier, a sample consumption of 5 μL and an incubation time of 2 min are enough for the sensor to detect a wide ALP activity range from 10 to 10,000 U/L, with a limit of detection of 5.70 U/L. This facile fabricated sensor provides a quick response, cost-effective and non-destructive approach for monitoring living adherent osteoblast cell activity and holds promise for ALP quantification in other biological systems and clinical samples.

The activity of alkaline phosphatase in breast cancer exosomes simplifies the biosensing design

This work addresses a biosensor combining the immunomagnetic separation and the electrochemical biosensing based on the intrinsic ALP activity of the exosomes. This approach explores for the first time two different types of biomarkers on exosomes, in a unique biosensing device combining two different biorecognition reaction: immunological and enzymatic. Besides, the intrinsic activity of alkaline phosphatase (ALP) in exosomes as a potential biomarker of carcinogenesis as well as osseous metastatic invasion is also explored. To achieve that, as an in vitro model, exosomes from human fetal osteoblasts are used. It is demonstrated that the electrochemical biosensor improves the analytical performance of the gold standard colorimetric assay for the detection of ALP activity in exosomes, providing a limit of detection of 4.39 mU L^-1, equivalent to 10⁵ exosomes μL^-1. Furthermore, this approach is used to detect and quantify exosomes derived from serum samples of breast cancer patients. The electrochemical biosensor shows reliable results for the differentiation of healthy donors and breast cancer individuals based on the immunomagnetic separation using specific epithelial biomarkers CD326 (EpCAM) combined with the intrinsic ALP activity electrochemical readout.

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.

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.

Overview of Optical and Electrochemical Alkaline Phosphatase (ALP) Biosensors: Recent Approaches in Cells Culture Techniques

Alkaline phosphatase (ALP), which catalyzes the dephosphorylation process of proteins, nucleic acids, and small molecules, can be found in a variety of tissues (intestine, liver, bone, kidney, and placenta) of almost all living organisms. This enzyme has been extensively used as a biomarker in enzyme immunoassays and molecular biology. ALP is also one of the most commonly assayed enzymes in routine clinical practice. Due to its close relation to a variety of pathological processes, ALP's abnormal level is an important diagnostic biomarker of many human diseases, such as liver dysfunction, bone diseases, kidney acute injury, and cancer. Therefore, the development of convenient and reliable assay methods for monitoring ALP activity/level is extremely important and valuable, not only for clinical diagnoses but also in the area of biomedical research. This paper comprehensively reviews the strategies of optical and electrochemical detection of ALP and discusses the electrochemical techniques that have been addressed to make them suitable for ALP analysis in cell culture.

Facile synthesis of core-shell CuS-Cu2S based nanocomposite for the high-performance glucose detection

Glucose detection is of great importance for the medical diagnosis, food biotechnology and pharmaceutical analysis. In this study, we synthesized a core-shell CuS-Cu₂S decorated carbon nanotube-graphene nanocomposite via a facile hydrothermal method. It exhibits great sensing performance towards glucose with wide linear range ranging from 0.001 to 2 mM, ultra-sensitivity of 1923 μA·cm^-2·mM^-1 and 0.33 μM detection limit in alkaline solutions. The excellent electrocatalytic activity originates from the synergistic effect between heterogeneous copper sulfides structures and carbon nanomaterials. Besides, the fabricate sensor also has great durability, selectivity and great potential for practical applications.

Alkaline phosphatase determination via regulation of enzymatically generated poly(thymine) as a template for fluorescent copper nanoparticle formation

We propose a new fluorometric method for alkaline phosphatase (ALP) determination. This method is based on the regulation of enzymatically generated poly(thymine) for the preparation of copper nanoparticles (CuNPs). 2'-Deoxythymidine 5'-triphosphate (dTTP) serves as the source for polymerization mediated by terminal deoxynucleotidyl transferase (TdT). This process generates poly(thymine), which acts as the template for synthesis of fluorescent CuNPs. However, if ALP catalyzes the hydrolysis of dTTP, the TdT-mediated polymerization will be disabled. This prevents the formation of CuNPs and causes a drop in fluorescence. The findings were used to design a sensitive and selective fluorometric method for ALP determination. A linear response in the activity range from 0.1 to 20 U L^-1 and a limit of quantification of 0.3 U L^-1 were obtained. The results indicate that the proposed method can be successfully applied to ALP assay in spiked diluted serum. This demonstrates the method's reliability and practicability. Graphical abstract A fluoromoetric method for alkaline phosphatase assay has been developed based on regulation of enzymatically generated poly(thymine) as template for the formation of fluorescent CuNPs.

Enzyme-triggeredin situformation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity

ALP-triggeredin situformation of Ag NPs with high oxidase-mimicking activity for colorimetric detection of alkaline phosphatase activity.

Photoelectrochemical determination of alkaline phosphatase activity based on a photo-excited electron transfer strategy

A sensitive photoelectrochemical (PEC) biosensor for determination of alkaline phosphatase (ALP) activity was constructed based on a photo-excited electron transfer strategy. Immobilization of CdTe quantum dots (QDs) on TiO₂ nanotube arrays (TNAs), addition of iron (III) and adenosine triphosphate (ATP) in turn can effectively adjust the photocurrent response of TNAs under visible light irradiation due to a photo-excited electron transfer process, and alkaline phosphatase (ALP) activity can be determined for its catalysis toward dephosphorylation of ATP. The preparation of CdTe QDs, construction of TNA/QD PEC biosensor and the mechanism of photo-excited electron transfer are investigated in the present work. Under the optimal experimental conditions, the TNA/QD PEC biosensor shows a low limits of detection (LODs) (0.05 U L^-1) and limits of quantification detection (LOQs) (0.15 U L^-1), wide linear range from 0.2 to 15 U L^-1, and good selectivity towards ALP determination, which has been successfully applied for human serum analysis with good precision (RSD ≤ 5.4%) and high accuracy (recovery rate, 91-112%).

Unlocking the hidden talent of DNA: Unexpected catalytic activity for colorimetric assay of alkaline phosphatase

Carboxylic acids have been efficiently used to activate H₂O₂ to form even more potent oxidant-peroxy acids through enzyme-catalyzed processes. By employing acetic acid as the activator, herein we report for the first time that cofactor-free DNA displays unexpected activity in H₂O₂-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) under mild conditions. A series of 10-nt oligonucleotides were rationally designed with various combinations of double nucleotides including TG, AG, CG, TA and AC respectively, which demonstrates that the catalytic performance of DNA is highly dependent upon the sequence composition, strand length and continuous nucleotides. Inspired by phosphate-induced inhibition effects on the formation of peracetic acid, an ultrasensitive assay was well-established for monitoring alkaline phosphatase (ALP) on the basis of double terminal-phosphorylated G-rich oligonucleotides. Phosphorylated DNA not only serves as the substrate for ALP-catalyzed hydrolysis, but also acts as the enzyme-like catalyst for signal amplification. Quantitative determination of ALP is realized in a linear range from 0.05 to 15 mU/mL, resulting in the limit of detection of 0.01 mU/mL. The rapid and reliable test also has great potential in analyzing serum samples for practical disease diagnosis.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.