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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. [ABSTRACT FROM AUTHOR]

In recent years, contrast agents have been widely used in imaging technology to improve quality. Nanoparticles have better in vivo detection capability than conventional molecular scale contrast agents. In this study, a new type of Au nanocages@PEG nanoparticles (AuNC@PEGs) with a strong X-ray absorption coefficient was synthesized as a contrast agent for computed tomography (CT) scan imaging. Results showed that AuNC@PEGs had good aqueous dispensation, low cytotoxicity, and strong X-ray absorption ability. Furthermore, in vivo studies have shown that the synthesized AuNC@PEGs have an evident contrast enhancement, long circulation time in the blood, and negligible toxicity in vivo. Therefore, the synthesized functionalized AuNC@PEGs in this study have great potential for clinical application in CT scan imaging. [ABSTRACT FROM AUTHOR]

Herein, papain-protected bimetallic gold/silver nanoclusters (Au/Ag NCs) were successfully synthesized and applied for the detection of ascorbate oxidase (AAO). The doping of papain-protected Au nanoclusters with Ag enhanced the fluorescence intensity with an intense red fluorescence peak at 617 nm, and the red-emitting Au/Ag nanoclusters were further used to monitor the AAO activity. The fluorescence of Au/Ag NCs could be quenched by hydrogen peroxide (H2O2) due to the generation of hydroxyl radicals (˙OH) from the reaction of Ag/Au nanoclusters and H2O2. However, the addition of ascorbic acid (AA) effectively reacted with the free radicals and caused the fluorescence recovery of the Au/Ag NCs. Furthermore, AAO could catalyze the oxidation of AA to form dehydro-ascorbate (DHA). As a result, there was not enough AA to consume the hydroxyl radicals, which resulted in a decrease in the fluorescence of the papain-capped Au/Ag NCs. Therefore, the AAO activity can be monitored by measuring the fluorescence intensity of the red-emitting Au/Ag NCs. Moreover, the developed method for AAO detection displayed a good linear relationship from 5 to 80 mU mL−1 and the detection limit was 1.72 mU mL−1. Thus, a simple and selective method for the determination of the AAO activity was constructed and satisfactory results were obtained in real sample detection. [ABSTRACT FROM AUTHOR]

In this work, a facile, label-free, and sensitive fluorometric strategy for detection of trypsin and its inhibitor was established on the basis of the fluorescence resonance energy transfer (FRET) between mercaptoundecanoic acid functionalized gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs) via protamine as a bridge. Protamine can trigger the aggregation of AuNPs and link AuNCs with aggregated AuNPs through electrostatic interaction. Compared with monodisperse AuNPs, the UV-vis absorption band of aggregated AuNPs overlapped considerably with the emission spectrum of AuNCs. Thus, the fluorescence of AuNCs was obviously quenched by the aggregated AuNPs through FRET. In the presence of trypsin, protamine was hydrolyzed into small fragments, leading to the deaggregation of AuNPs and breaking of the short distance between AuNPs and AuNCs, so the FRET process was inhibited, and the fluorescence of AuNCs was recovered. The increase in the fluorescence intensity of AuNCs was directly related to the amount of trypsin. Hence trypsin can be determined on the basis of the variation of fluorescence intensity, with a linear range of 5-5000 ng mL-1 and a detection limit of 1.9 ng mL-1. In addition, this system was used for the detection of trypsin inhibitor by application of the inhibitor isolated from soybean as a model. The sensing method was applied for trypsin detection in human urine and commercial multienzyme tablet samples with satisfactory results.ᅟ [ABSTRACT FROM AUTHOR]

Novel multielement Au/La-SrTiO3 microspheres were synthesized by a solvothermal method using monodisperse gold and La-SrTiO3 nanocrystals as building blocks. The porous Au/La-SrTiO3 microspheres had a large surface area of 94.6 m2 g−1. The stable confined Au nanoparticles demonstrated strong surface plasmon resonance effect, leading to enhanced absorption in a broad UV/Vis/NIR range. Doping of rare-earth metal La also broadened the absorption band to the visible region. Both the conduction and valence bands of Au/La-SrTiO3 microspheres thus show favorable potential for proton reduction under visible light. The superimposed effect of Au nanoparticles and La doping in Au/La-SrTiO3 microspheres led to high photocurrent density in photoelectrochemical water splitting and good photocatalytic activity in photodegradation of rhodamine B. The photocatalytic activities are in the order of the following: Au/La-SrTiO3 microspheres>Au/SrTiO3 microspheres>La-SrTiO3 microspheres>SrTiO3 microspheres. [ABSTRACT FROM AUTHOR]

• A sandwich-type electrochemical immunosensor with good recovery, sensitivity, reliability and selectivity was constructed. • PEDOT:PSS and AuNPs resulted in an outstanding conductive platform. • ZIF-8 was employed as a nice signal carrier and a novel signal amplification strategy achieved. • The electrochemical immunosensor exhibited a low detection limit of 0.09 ng mL−1 for the detection of p53 protein. In this work, we fabricated a novel sandwich-type electrochemical immunosensor for quantitative and ultra-sensitive determination of tumor suppressor protein p53 by signal amplification strategy. Conductive polymers poly (3, 4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) has significantly effect on enhancing charge transfer and markedly increases the sensitivity of electrochemical immunosensing. Gold nanoparticles (AuNPs) as high conductivity nanocarriers were also used to capture monoclonal antibodies (Ab 1) due to their large specific surface areas. In addition, pH responsive zeolitic imidazolate framework (ZIF-8) was used to load the redox probe 2, 3-diaminophenazine (DAP) and the secondary antibodies (Ab 2) to form a sensitive-type ZIF-8–DAP–Ab 2 immunoprobe. After the sandwich-type immunoassay with the free p53 protein, with the release of probe DAP after the electrochemical signal amplificated by PEDOT:PSS and AuNPs, the ultra-sensitive and quantitative determination of p53 protein was realized with working range of 1–120 ng mL−1 and low detection limit of 0.09 ng mL−1. Besides, the fabricated electrochemical immunosensor exhibited good recovery, high sensitivity, reliability, and selectivity. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a split aptamer based fluorescence resonance energy transfer (FRET) platform was constructed for the determination of adenosine deaminase (ADA) activity by using gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs). A single adenosine triphosphate (ATP) aptamer was split into two fragments (referred to as P1 and P2). P1 was covalently attached to the AuNCs at the 5′ end (P1-AuNCs), and P2 was labeled with AuNPs at the 3′ end (P2-AuNPs). In the presence of ATP, ATP bound with the two fragments with high affinity to link P1-AuNCs and P2-AuNPs together, thus the fluorescence of P1-AuNCs was quenched via FRET from P1-AuNCs to P2-AuNPs. With the addition of ADA, ATP was transformed into inosine triphosphate (ITP), and then P1 and P2 were released to cause the fluorescence recovery of the system. So a split aptamer based FRET platform for ADA detection can be established via the fluorescence intensity change of the system. This platform showed a good linear relationship between the fluorescence intensity and ADA concentration in the range of 2–120 U L−1, and the limit of detection (LOD) was 0.72 U L−1. Moreover, the detection of ATP in human serum sample demonstrated the accuracy and applicability of the method for ADA detection in real sample. Graphical abstract A split aptamer based fluorescence resonance energy transfer (FRET) sensing platform was constructed for adenosine deaminase (ADA) activity detection by utilizing gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs). fx1 Highlights • A split aptamer based sensing platform for ADA detection was proposed. • Split ATP aptamers (P1 and P2) were designed to synthesize P1-AuNCs and P2-AuNPs complexes. • The specific binding of ATP to its split aptamers triggered the FRET from P1-AuNCs to P2-AuNPs. • FRET process was restrained when ADA transform ATP to ITP that had no ability to combine with split ATP aptamers. • The platform was successfully applied for ADA detection in human serum sample. [ABSTRACT FROM AUTHOR]

As one of primary biomarkers of ovarian cancer in early stages, β-galactosidase (β-Gal) is significant in the discovery and diagnosis of the disease. In this work, we constructed a multi-signal sensing platform based on silicon nanoparticles (Si NPs) for β-Gal activity determination. When β-Gal was introduced to the sensing system, 2-Nitrophenyl β-D-galactopyranoside (ONPG) could be converted to o -Nitrophenol (o-NP), which had a characteristic absorption peak at 416 nm and the colorless solution turned yellow. The fluorescence emission of Si NPs at 450 nm can be greatly quenched by o-NP as a consequence of inner filter effect (IFE). This dual-signal fluorometric and colorimetric determination approach could be utilized to detect β-Gal in the range of 2–120 U/L and 6–120 U/L. The limits of detection were 1.36 U/L and 1.07 U/L, respectively. This sensing platform could be successfully utilized to detect β-Gal in real samples. Additionally, a visual detection method was designed to achieve quantitative analysis of β-Gal with the assistance of the smartphone. A multi-signal fluorometric-colorimetric and smartphone-assisted method for β-Gal activity detection was developed by taking advantage of the fluorescence quenching of silicon nanoparticles (Si NPs) by o -Nitrophenol (o-NP), which has a characteristic absorption peak at 416 nm and is yellow observed by naked eyes. [Display omitted] • A dual-signal fluorometric and colorimetric system was established for β-Gal activity detection. • Simple materials and operations were needed in the construction of the system. • A convenient smartphone-assisted detection method was developed. • The sensing system was applied for β-Gal activity detection in human serum. [ABSTRACT FROM AUTHOR]