Lingyang Zhang

Preparation of Gold–Carbon Dots and Ratiometric Fluorescence Cellular Imaging

In this study, we synthesized novel gold-carbon dots (GCDs) with unique properties by microwave-assisted method. The characterization of high-resolution transmission electron microscope (HRTEM), XRD, high-angle annular dark field scanning transmission electron microscope (HAADF-STEM), and energy dispersive spectrometer demonstrates that GCDs are composed of carbon and Au. Tiny Au clusters are dispersed in a 2 nm-size carbon skeleton, which integrates the properties of typical CDs and gold nanoclusters (AuNCs), displaying fascinating peroxidase-like activity and single excitation/dual emission. Dual emission of the GCDs exhibits different fluorescent response to the target species and enables the GCDs to be exploited for sensing and bioimaging. The highly photostable and biocompatible GCDs were applied to dual fluorescent imaging for breast cancer cells and normal rat osteoblast cells under a single excitation. Moreover, ratiometric fluorescence imaging was used to monitor Fe(3+) level in normal rat osteoblast cells.

Carbon dots as a fluorescent probe for label-free detection of physiological potassium level in human serum and red blood cells.

A unique photoluminescence carbon dots (CDs) with larger size were prepared by microwave-assisted method. Complex functional groups on the surface of the CDs facilitate the nanoparticles to form affinity with some metal ions. Taking advantage of the effective fluorescence quenching effect of K(+), a highly sensitive CD-based fluorescence analytical system for label-free detection of K(+) with limit of detection (LOD) 1.0×10(-12) M was established. The concentrations of potassium ion in biological samples such as human serum are usually found at millimolar levels or even higher. The proposed method begins with a substantial dilution of the sample to place the K(+) concentration in the dynamic range for quantification, which covers 3 orders of magnitude. This offers some advantages: the detection of K(+) only needs very small quantities of biological samples, and the dilution of samples such as serum may effectively eliminate the potential interferences that often originate from the background matrix. The determined potassium levels were satisfactory and closely comparable with the results given by the hospital, indicating that this fluorescent probe is applicable to detection of physiological potassium level with high accuracy. Compared with other relative biosensors requiring modified design, bio-molecular modification or/and sophisticated instruments, this CD-based sensor is very simple, cost-effective and easy detection, suggesting great potential applications for successively monitoring physiological potassium level and the change in biological system.

Detection of Fe(III) and bio-copper in human serum based on fluorescent AuAg nanoclusters

In this study, a fluorescence assay for the successive determination of Fe3+ and Cu2+ ions based on the quenching fluorescence of composite AuAg nanoclusters (AuAg NCs) was developed. Using this binary fluorescence sensor, the Fe(III) level in a human serum sample can be directly detected without pretreatment. After the nitrification of human serum, the bio-copper level in human serum may be measured with a quick response. Human serum samples were analyzed, and the average concentration of Fe(III) and bio-copper were found to be 2.33 × 10−5 and 2.91 × 10−5 M, respectively. This assay was not only sensitively responsive to blood iron(III) but also to serum copper, suggesting significant potential applications for successively monitoring the Fe(III) and bio-copper levels, and their changes during the progression of a biological process.

Synthesis of biocompatible AuAgS/Ag2S nanoclusters and their applications in photocatalysis and mercury detection

In this paper, a facile approach for preparation of AuAgS/Ag2S nanoclusters was developed. The unique AuAgS/Ag2S nanoclusters capped with biomolecules exhibit interesting excellent optical and catalytic properties. The fluorescent AuAgS/Ag2S nanoclusters show tunable luminescence depending on the nanocluster size. The apoptosis assay demonstrated that the AuAgS/Ag2S nanoclusters showed low cytotoxicity and good biocompatibility. Therefore, the nanoclusters can be used not only as a probe for labeling cells but also for their photocatalytic activity for photodegradation of organic dye. Moreover, a highly selective and sensitive assay for detection of mercury including Hg2+ and undissociated mercury complexes was developed based on the quenching fluorescent AuAgS/Ag2S nanoclusters, which provides a promising approach for determining various forms of Hg in the mercury-based compounds in environment. These unique nanoclusters may have potential applications in biological labeling, sensing mercury, and photodegradation of various organic pollutants in waste water.Graphical Abstract

Peroxidase-Like Activity of Ethylene Diamine Tetraacetic Acid and Its Application for Ultrasensitive Detection of Tumor Biomarkers and Circular Tumor Cells

Ethylene diamine tetraacetic acid (EDTA) is such a powerful chelating agent that it may form stable complexes with most metal ions, which has wide applications in industry, agriculture, environment, and pharmaceutical technology. Recently, EDTA was found to enhance the photocatalytic property of some materials. Inspired by this fact of EDTA in the photocatalytic role, we further investigated the photocatalytic property of EDTA and found much the same as that of natural horseradish peroxidase (HRP). This significant discovery of peroxidase-like property may extend the applications of conventional EDTA in life science. A novel and colorimetric sensor based on the peroxidase-like EDTA and unique gold nanorods (GNRs) was designed. Under light irradiation, EDTA may catalyze decomposition of hydrogen peroxide and in situ regulate the longitudinal plasmon wavelength (LPW) of GNRs, displaying various color solution as a read-out means. This colorimetric nanosensor has a great potential to develop into a platform to quantitatively determine analytes as long as the specific antibodies against them were available. Biomarkers of different diseases, such as breast cancer and prostate cancer, were detected with high accuracy. Moreover, combined with immunomagnetic separation of circulating tumor cells (CTCs) from blood, a visual read-out for detection of CTCs was established, which has promising applications in clinical diagnosis, environmental monitoring, and food quality control only using naked eyes.

Successive detection of glucose and bio-copper in human serum based on a multiplex biosensor of gold nanorods

In this paper, a promising combined assay for the successive detection of blood glucose and sera copper levels based on etching of gold nanorods (GNRs) was developed. A hydroxyl radical-enhanced GNR oxidation under ultraviolet irradiation facilitates the establishment of a plasmonic biosensor that may quickly detect blood glucose. A linear relationship between the change of the plasmonic wavelength and the glucose concentration was found (Δλ = 4.2284 + 132.0c) in the range of 0.23 to 0.928 mM and the LOD was 0.45 μM. The determination of blood glucose using this proposed method was satisfactory and closely comparable to the results given by the local hospital. On the other hand, a blue-shift of the longitudinal plasmon wavelength induced by various forms of copper in the presence of Na2S2O3 provides a sensitive approach to detect the total copper level in a biological sample. The copper levels of human sera were measured and corroborated by flame atomic absorption spectrometry, which confirms that this approach might be applicable for bio-copper analysis with high accuracy. A combined assay for the successive detection of the blood glucose level and serum copper was subsequently developed. Compared to other related biosensors requiring a modified design, bio-molecular modification or/and sophisticated instruments, the dual glucose and copper sensor is very simple, cost-effective and easy to use for detection, suggesting great potential applications for successively monitoring blood glucose and copper concentrations and their changes during the progression of diabetes.

Alternate release of different target species based on the same gold nanorods and monitored by cell imaging.

In this study, a strategy for load and release of different kinds of molecules on the same gold nanorods (GNRs) was developed. An anticancer drug, doxorubicin hydrochloride (DOX), was firstly chemically conjugated on the GNRs. To efficiently load another type of target molecules DNA on the same GNRs, a polyelectrolyte Poly (ethylene imine) (PEI) was adsorbed on the GNR@DOX to form GNR@DOX@PEI. Then, the positive charge GNR@DOX@PEI allows the GNR conjugates to interact with negative charged DNA by an electrostatic interaction, enabling their full conjugation. A platform to load two kinds of target molecules conjugated on the same GNRs was fabricated. On the other hand, selective and sequential release of the different target species may be triggered by chemical reaction and near infrared (NIR) laser. The release of DOX was achieved by Na2S2O3 reacting with GNRs and the discharge of DNA conjugated on the GNR@DOX@PEI was accomplished by local-heating using NIR laser triggered release. Furthermore, the selective and alternate release of different target species from the GNRs inside MCF-7 cells was monitored by fluorescent imaging, providing a potential synergistic cancer treatment.