Molybdenum disulfide (MoS2) has attracted increasing research interest recently due to its unique physical, optical and electrical properties, correlated with its 2D ultrathin atomic-layered ...structure. Until now, however, great efforts have focused on its applications such as lithium ion batteries, transistors, and hydrogen evolution reactions. Herein, for the first time, MoS2 nanosheets are discovered to possess an intrinsic peroxidase-like activity and can catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce a color reaction. The catalytic activity follows the typical Michaelis-Menten kinetics and is dependent on temperature, pH, H2O2 concentration, and reaction time. Based on this finding, a highly sensitive and selective colorimetric method for H2O2 and glucose detection is developed and applied to detect glucose in serum samples. Moreover, a simple, inexpensive, instrument-free and portable test kit for the visual detection of glucose in normal and diabetic serum samples is constructed by utilizing agarose hydrogel as a visual detection platform.
Novel highly fluorescent (FL) metal–organic frameworks (MOFs) have been synthesized by encapsulating branched poly-(ethylenimine)-capped carbon quantum dots (BPEI-CQDs) with a high FL quantum yield ...into the zeolitic imidazolate framework materials (ZIF-8). The as-synthesized FL-functionalized MOFs not only maintain an excellent FL activity and sensing selectivity derived from BPEI-CQDs but also can strongly and selectively accumulate target analytes due to the adsorption property of MOFs. The selective accumulation effect of MOFs can greatly amplify the sensing signal and specificity of the nanosized FL probe. The obtained BPEI-CQDs/ZIF-8 composites have been used to develop an ultrasensitive and highly selective sensor for Cu2+ ion, with a wide response range (2–1000 nM) and a very low detection limit (80 pM), and have been successfully applied in the detection of Cu2+ ions in environmental water samples. It is envisioned that various MOFs incorporated with FL nanostructures with high FL quantum yields and excellent selectivity would be designed and synthesized in similar ways and could be applied in sensing target analytes.
A novel sensing system has been designed for Cu2+ ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu2+ ...ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs’ FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu2+ with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu2+ ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.
An easy bottom–up method for the preparation of photoluminescent (PL) graphene quantum dots (GQDs) and graphene oxide (GO) has been developed by tuning the carbonization degree of citric acid and ...dispersing the carbonized products into alkaline solutions. The GQDs are nanosheets ∼15nm in width, and 0.5–2.0nm in thickness. They show a relatively strong (9.0%) PL quantum yield and an excitation-independent PL emission activity. In contrast, the GO nanostructures consist of sheets that are hundreds of nanometers in width and ∼1nm in height. They exhibit a relatively weak (2.2%) PL quantum yield and an excitation-dependent PL emission activity.
A novel flow-through multiplexed immunoassay protocol for simultaneous electrochemical determination of carcinoembryonic (CEA) and alpha-fetoprotein (AFP) in biological fluids was designed using ...biofunctionalized magnetic graphene nanosheets (MGO) as immunosensing probes and multifunctional nanogold hollow microspheres (GHS) as distinguishable signal tags. The probes were fabricated by means of co-immobilization of primary anti-CEA (Ab1) and anti-AFP (Ab2) antibodies on the Fe3O4 nanoparticle-coated graphene nanosheets (MGO-Ab1,2). The reverse-micelle method was used for the synthesis of distinguishable signal tags by encapsulation of horseradish peroxide (HRP)-thionine and HRP-ferrocene into nanogold hollow microspheres, respectively, which were utilized as labels of the corresponding GHS-Ab1 and GHS-Ab2. A sandwich-type immunoassay format was employed for the online detection of CEA and AFP by coupling a flow-through detection cell with an external magnet. The assay was based on the catalytic reduction of H2O2 at the various peak potentials in the presence of the corresponding mediators. Experimental results revealed that the multiplexed electrochemical immunoassay enabled the simultaneous monitoring of AFP and CEA in a single run with wide working ranges of 0.01–200 ng mL–1 for AFP and 0.01–80 ng mL–1 for CEA. The detection limits (LODs) for both analytes at 1.0 pg mL–1 (at 3s B) were very low. No obvious nonspecific adsorption and cross-talk were observed during a series of analyses to detect target analytes. Intraassay and interassay coefficients of variation were <10%. Importantly, the methodology was evaluated for the analysis of clinical serum specimens, receiving a good correlation between the flow-through multiplexed electrochemical immunoassay and an electrochemiluminescence method as a reference.
Two-dimensional graphite-like carbon nitride nanosheets (g-C3N4 NSs) were hybridized with gold nanoparticles (Au NPs) to construct an electrochemiluminescence (ECL) immunosensor. The prepared Au ...NP-functionalized g-C3N4 NS nanohybrids (Au-g-C3N4 NHs) exhibit strong and stable cathodic ECL activity compared to g-C3N4 NSs due to the important roles of Au NPs in trapping and storing the electrons from the conduction band of g-C3N4 NSs, as well as preventing high energy electron-induced passivation of g-C3N4 NSs. On the basis of the improved ECL stability and ECL peak intensity of the Au-g-C3N4 NHs, a novel ECL immunosensor was developed to detect carcinoembryonic antigen (CEA) as a model target analyte. The ECL immunosensor has a sensitive response to CEA in a linear range of 0.02–80 ng mL–1 with a detection limit of 6.8 pg mL–1. Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.
A novel reverse colorimetric immunoassay (RCIA) strategy was for the first time designed and utilized for sensitive detection of low-abundance protein (prostate-specific antigen, PSA, used in this ...case) in biological fluids by coupling highly catalytic efficient catalase with magnetic bead-based peroxidase mimics. To construct such a RCIA system, two nanostructures including magnetic beads and gold nanoparticles were first synthesized and functionalized with anti-PSA capture antibody and catalase/anti-PSA detection antibody, respectively. Thereafter, a specific sandwich-type immunoassay format was employed for determination of PSA by using functional gold nanoparticles as enzymatic bioreactors and anti-PSA-conjugated magnetic beads as a colorimetric developer. The carried catalase, followed by the sandwiched immunocomplex, partially consumed the added hydrogen peroxide in the detection solution, which slowed down the catalytic efficiency of magnetic bead-based peroxidase mimics toward TMB/H2O2, thereby weakening the visible color and decreasing the colorimetric density. Different from conventional colorimetric immunoassay, the RCIA method determined the residual hydrogen peroxide in the substrate after consumption. Under the optimal conditions, the developed RCIA exhibited a wide dynamic range of 0.05–20 ng mL–1 toward PSA with a detection limit of 0.03 ng mL–1 at the 3S blank level. Intra- and interassay coefficients of variation were below 6.1% and 9.3%, respectively. Additionally, the methodology was further validated for the analysis of 12 PSA clinical serum specimens, giving results in good accordance with those obtained by the commercially available enzyme-linked immunosorbent assay (ELISA) method.
The development of signal-amplified colorimetric immunoassay relies on the design of highly efficient signal-transduction tags. One promising route is to exploit a novel enzyme mimetic system as the ...signal label. Herein, we report that urchin-like (gold core)@(platinum shell) nanohybrids (Au@PtNHs) can be utilized as a highly efficient peroxidase mimetic system for in situ amplified colorimetric immunoassay of prostate-specific antigen (PSA, one kind of tumor marker). Initially, urchin-like Au@PtNHs were discovered to outperform horseradish peroxidase (HRP) by a vast margin in terms of the turnover number toward hydrogen peroxide (H2O2)-3,3’,5,5’-tetramethylbenzidine (TMB) system and the stability against high temperatures and HRP inhibitors. Based on this discovery, the assay was simply carried out on a capture antibody-immobilized microplate by using the Au@PtNH-labeled detection antibody as a signal-transduction tag with a sandwich-type assay mode. The colorimetric signal stemmed from the labeled Au@PtNHs toward catalytic oxidation of TMB–H2O2 system. Experimental results indicated that the Au@PtNH-based colorimetric immunoassay could display a good colorimetric response toward PSA in the dynamic working range of 5–500pgmL−1 with a low detection limit of 2.9pgmL−1. Meanwhile, the developed immunoassay exhibited good precision and reproducibility, high specificity and acceptable accuracy for the detection of clinical serum samples. These results open up a new horizon for the development of highly sensitive, highly stable and inexpensive non-enzyme immunoassay platforms as an alternative to conventional enzyme-based immunoassay platforms.
•We report a new peroxidase mimetic system for highly efficient colorimetric immunoassay.•Urchin-like (gold core)@(platinum shell) porous nanohybrid was used as the peroxidase mimic.•The nanohybrid could exhibit higher catalytic activity than that of commercialized horseradish peroxidase.
Free chlorine was found to be able to destroy the passivated surface of the graphene quantum dots (GQDs) obtained by pyrolyzing citric acid, resulting in significant quenching of their fluorescence ...(FL) signal. After optimizing some experimental conditions (including response time, concentration of GQDs, and pH value of solution), a green and facile sensing system has been developed for the detection of free residual chlorine in water based on FL quenching of GQDs. The sensing system exhibits many advantages, such as short response time, excellent selectivity, wide linear response range, and high sensitivity. The linear response range of free chlorine (R 2 = 0.992) was from 0.05 to 10 μM. The detection limit (S/N = 3) was as low as 0.05 μM, which is much lower than that of the most widely used N-N-diethyl-p-phenylenediamine (DPD) colorimetric method. This sensing system was finally used to detect free residual chlorine in local tap water samples. The result agreed well with that by the DPD colorimetric method, suggesting the potential application of this new, green, sensitive, and facile sensing system in drinking water quality monitoring.
The metal-organic framework (MOF) was first utilized as the sensing platform for assaying biomolecules. It has also been demonstrated that this novel strategy is effective and reliable for detection ...of HIV DNA and thrombin with high sensitivity and selectivity.
