Haichao Dai

Label-free turn-on fluorescent detection of melamine based on the anti-quenching ability of Hg2+ to gold nanoclusters

In this work, we proposed a facile, environmentally friendly and cost-effective assay for melamine with BSA-stabilized gold nanoclusters (AuNCs) as a fluorescence reader. Melamine, which has a multi-nitrogen heterocyclic ring, is prone to coordinate with Hg(2+). This property causes the anti-quenching ability of Hg(2+) to AuNCs through decreasing the metallophilic interaction between Hg(2+) and Au(+). By this method, detection limit down to 0.15 µM is obtained, which is approximately 130 times lower than that of the US food and Drug Administration estimated melamine safety limit of 20 µM. Furthermore, several real samples spiked with melamine, including raw milk and milk powder, are analyzed using the sensing system with excellent recoveries. This gold-nanocluster-based fluorescent method could find applications in highly sensitive detection of melamine in real samples.

A graphene oxide based biosensor for microcystins detection by fluorescence resonance energy transfer

Water safety is one of the most pervasive problems afflicting people throughout the world. Microcystin, a hepatotoxin produced by cyanobacteria, poses a growing and serious threat of water safety. According to World Health Organization (WHO), the limit of content of microcystin-LR (MC-LR) in drinking water is as low as 1 μg/L; it is thus necessary to explore a sensitive method for the trace detection of microcystins (MCs). Based on the observation of gold nanoparticles (Au NPs) induced graphene oxide (GO) fluorescence quenching, a reliable biosensor was developed here for microcystins detection. MCs could be attached on Au NPs through the interaction with single strand-DNA (ss-DNA) modified on Au NPs, which formed Au-DNA-MCs complexes. These MCs in the complexes could be immunologically recognized by the antibodies adsorbed on GO sheets, as a result, Au NPs were close enough to quench the photoluminescence of GO by the fluorescence resonance energy transfer (FRET). The fluorescence intensity decreased with the increase of MCs as more Au NPs linked onto GO surface. The limit of detection was 0.5 and 0.3 μg/L for microcystin-LR and microcystin-RR (MC-RR), respectively, which satisfies the strictest standard of WHO. Well defined results were also obtained in natural lake water and the specificity experiment. The antibody used here could recognize Adda group, the conservative part of MCs, which allowed the biosensor to detect both single toxin and the total content of MCs existing in the water sample.

Carbon dots based fluorescent sensor for sensitive determination of hydroquinone

In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H2Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H2Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H2Q-quinone. Based on the above principle, a novel C-dots based fluorescent probe has been successfully applied to detect H2Q. Under the optimal condition, detection limit down to 0.1 μM is obtained, which is far below U.S. Environmental Protection Agency estimated wastewater discharge limit of 0.5 mg/L. Moreover, the proposed method shows high selectivity for H2Q over a number of potential interfering species. Finally, several water samples spiked with H2Q are analyzed utilizing the sensing method with satisfactory recovery. The proposed method is simple with high sensitivity and excellent selectivity, which provides a new approach for the detection of various analytes that can be transformed into quinone.

Facile fabrication of CuO nanowire modified Cu electrode for non-enzymatic glucose detection with enhanced sensitivity

In this paper the fabrication of CuO nanowires (CuO NWs) by a facile two-step method is reported. Cu(OH)2 nanowires (Cu(OH)2 NWs) on a copper surface were prepared at room temperature by a simple solution-based procedure, and subsequent calcinations of Cu(OH)2 NWs led to the formation of CuO NWs. The morphologies and structures of Cu(OH)2 NWs and CuO NWs were characterized by scanning electron microscopy and X-ray diffraction. Electrochemical measurements showed that the CuO NWs modified Cu electrode exhibited good electrocatalytic behavior for the detection of glucose with a wide linear range from 2 μM to 3.56 mM (R2 = 0.9984), a low detection limit down to 0.05 μM, and a high sensitivity of 1886.3 μA mM−1 cm−2. The sensor also displayed a high selectivity, an acceptable reproducibility, an excellent long-term stability and good repeatability. Moreover, the as-prepared sensor has great potential in practical applications.

Facile synthesis of Prussian blue @ gold nanocomposite for nonenzymatic detection of hydrogen peroxide

A sensitive hydrogen peroxide (H2O2) sensor was fabricated based on a Prussian blue @ gold nanocomposite (PB@Au). Au nanoparticles (Au NPs) were first electrodeposited on a glassy carbon electrode (GCE) to increase the conductivity and to catalyze the chemical deposition of PB. Electrochemical measurements showed that the PB@Au modified electrode exhibited good electrocatalytic behavior for the detection of H2O2 with a wide linear range from 2 μM to 8.56 mM (R2 = 0.9980), a low detection limit down to 0.1 μM (S/N = 3), and a high sensitivity of 39.72 μA mM−1. The sensor also displayed a good anti-interference ability, an acceptable reproducibility, an excellent long-term stability and good repeatability. The desirable recoveries achieved in disinfected fetal bovine serum verified that the developed sensor could have a potential use in the detection of H2O2 in real samples. Moreover, the operating simplicity and low expense of the fabrication made the as-prepared electrode attractive.

Highly sensitive and rapid visual detection of ricin using unmodified gold nanoparticle probes

Herein, a sensitive and selective colorimetric biosensor for the detection of ricin was demonstrated with a 40-mer ricin-binding aptamer (RBA) as recognition element and unmodified gold nanoparticles (AuNPs) as probe. The sensitivity of the assay was greatly improved after optimizing several key parameters such as the amount of aptamer adsorbed on AuNPs, the concentration of NaCl, and the reaction time after adding NaCl. The linear range for the current analytical system was from 0.31 nM to 11.55 nM. The corresponding limit of detection (LOD) was 0.31 nM. Some different proteins such as thrombin (Th), horseradish peroxidase (HRP), lysozyme (Lys), glucose oxidase (GOx), and bovine albumin (BSA) showed no or just a little interference in the determination of ricin. This colorimetric aptasensor is superior to the other conventional methods owing to its simplicity, low cost, high sensitivity and detection with the naked eye, which can be used in real samples.

CuO nanothorn arrays on three-dimensional copper foam as an ultra-highly sensitive and efficient nonenzymatic glucose sensor

A CuO nanothorns/Cu foam (NTs-CuO/Cu foam) was synthesized using a low-cost and facile method. The morphology and composition of the NTs-CuO/Cu foam were characterized using SEM, TEM and XRD. Copper foam as the current collector played a key role in the formation of the NTs-CuO/Cu foam. The CuO nanothorns were freely grown on copper foam, and can make contact with the underneath conductive copper foam directly. The NTs-CuO/Cu foam was used as an electrocatalyst for the detection of glucose in an electrochemical sensor. The CuO nanothorns/Cu foam electrode shows an extremely high sensitivity of 5.9843 mA mM−1 cm−2 and a low detection limit of 0.275 μM based on a signal to noise ratio of 3. Due to its excellently high sensitivity, stability and anti-interference ability, the NTs-CuO/Cu foam will be a promising material for constructing practical non-enzymatic glucose sensors.

Fabrication of cuprous sulfide nanorods supported on copper foam for nonenzymatic amperometric determination of glucose and hydrogen peroxide

Cu2S nanorods supported on three-dimensional copper foam (Cu2S NRs@Cu foam) are in situ prepared by a low-cost and facile method. The structural and morphological characterization of the Cu2S NRs@Cu foam is executed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The high conductivity of copper foam as a current collector can facilitate charge and mass transfer, and the copper foam with an open framework provides large amounts of anchoring sites for the deposition of Cu2S NWs during the synthesis of the Cu2S NRs@Cu foam. Consequently, the Cu2S NRs@Cu foam works as an electrocatalyst for the detection of glucose and H2O2. Electrochemical measurements of the biosensor show an extremely high sensitivity of 11.7508 mA mM−1 cm−2 and a low detection limit of 0.07 μM for the electrocatalytic oxidation of glucose. The nonenzymatic sensor also exhibits a good response toward hydrogen peroxide with a high sensitivity of 1.686 mA mM−1 cm−2. The detection limit is calculated to be 0.2 μM. This method provides an efficient and promising strategy for the construction of practical non-enzymatic glucose and hydrogen peroxide sensors.

A new method to determine the thickness of platinum nanofilm simply by measuring its electrical resistance

In this report, it was found that the Napierian logarithm of the electrical resistance is proportional to the reciprocal thickness for the platinum nanofilms. A new method was proposed to determine the thickness of platinum nanofilm simply by measuring its electrical resistance, which is fast and cost effective.