Hong Zhi Zhang

Highly fluorescent carbon dots as selective and visual probes for sensing copper ions in living cells via an electron transfer process

As an integral part of many important enzymes, Cu2+ is involved in a number of vital biological processes, which is linked to the oxidative damage and environmental contamination when Cu2+ is excessive. In this work, Cu2+ can be captured by the amino groups of carbon dots (CDs) to form complexes, resulting in a strong fluorescence quenching of CDs via a nonradiative electron transfer process, which offered a rapid, visual, and selective methodology for Cu2+ detection. The probe exhibited a wide response concentration range (0.01-2μM) to Cu2+ with a detection limit of 6.7nM. Significantly, the CDs presented excellent biocompatibility and high photostability, which were applicable for the visualization of Cu2+ dynamic invasion into living cells and Tilapia mossambica. Furthermore, the toxicity of Cu2+ ions to living cells could be inhibited with CDs by the formation of complexes.

Plasmonic platforms for colorimetric sensing of cysteine

Abstract Cysteine plays a crucial role in physiological processes, as well as in the food, pharmaceutical, and even personal care industries, which is of great significance to control its concentration. Plasmonic nanomaterials have attracted increasing interest in colorimetric sensing, due to their outstanding optical, chemical, and catalytic properties. Their colors, derived from the absorption of the localized surface plasmon resonance (LSPR), strongly depend on the shape, size, constituent, and aggregates states, which could be tuned by cysteine. This review highlights the recent advances in cysteine detection with plasmonic nanoparticles as colorimetric platforms, wherein the colors of nanomaterials change upon the introduction of cysteine, which could be easily followed by the naked eye without requiring any instrumentation. The selective and sensitive detection mechanisms are discussed. The presence of cysteine could adjust the shape, size, constituent, and interparticle distance of nanomaterials, leading to the color transformation. In addition, the introduction of cysteine could adjust the catalytic capability of nanomaterials, resulting in the color variance. Based on those mechanisms, the colorimetric detection of cysteine could be achieved in a facile way. Finally, challenges and future perspectives are outlined.

Heparin sodium-selective ‘on–off’ and lysine-selective ‘off–on’ fluorescence switching of cadmium telluride quantum dots and their analytical applications

Sensing biomolecules such as heparin sodium and lysine are of great significance. In this work, a “turn-off–on” fluorescence switching of cadmium telluride quantum dots (CdTe QDs) was designed for both heparin sodium and lysine. Even though both heparin sodium and thioglycolic acid (TGA)-capped CdTe QDs are negatively charged, they are capable of forming a self-assembly and even aggregates through hydrogen bonding, depending on the concentration of heparin sodium, which leads to the sensitive fluorescence quenching of CdTe QDs. Thus, a fluorescence ‘turn-on’ analytical method for heparin sodium sensing could be established with a detection range of 0.200–5.000 μg mL−1 and the detection limit was 0.033 μg mL−1, which is applicable to determining heparin sodium in injection samples. Whats more, a sensitive and selective “turn-off–on” nanosensor was developed for lysine analysis with the detection range of 2–200 μmol L−1 and the detection limit as low as 0.146 μmol L−1. This approach offers a new, simple, fast and selective method for determining heparin sodium and lysine.

Stable gold nanoparticles as a novel peroxidase mimic for colorimetric detection of cysteine

In this work, a novel method for colorimetric detection of cysteine was proposed based on the inhibition of peroxidase-like behavior of AuNPs. Kiwi juice prepared gold nanoparticles presented strong catalytic activity, which could catalyze H2O2–TMB to generate a blue product, resulting in strong absorption at 650 nm. In HAc–NaAc (pH 4.0) buffer, cysteine induced the aggregation of gold nanoparticles through covalent Au–S bonds and electrostatic as well as hydrogen bonding, leading to the reduction of the catalytic activity of gold nanoparticles with a weakened blue color product and a lower absorbance. Under optimal conditions, the concentrations of cysteine were proportional to the degree of reduced absorbance. This approach offers a new, simple, sensitive and selective assay for cysteine.

Selective colorimetric analysis of spermine based on the cross-linking aggregation of gold nanoparticles chain assembly

A selective colorimetric assay for spermine was proposed in this work. In a weak alkaline medium, the conformational structure of double-stranded calf thymus DNA (ctDNA) was loosened to install gold nanoparticles (AuNPs) into chains. While, the chain assembly of AuNPs could form cross-linking aggregates when spermine was present, which was attributed to the electrostatic interaction between the positive change of spermine and negative change both of AuNPs and ctDNA, as well as the groove binding between ctDNA and spermine. Under the optimum conditions, the aggregation degree of AuNPs was proportional to the concentration of spermine in the range of 0.1-2.0μM with a limit of detection of 11.6nM. More interestingly, AuNPs changed from red to purple and even to blue depending on the concentration of spermine, which could be developed as the colorimetric analysis of spermine. ctDNA-AuNPs assembly was demonstrated as a novel visual probe for the specific sensing of spermine with high specificity and sensitivity.

Highly selective detection of spermine in human urine via a nanometal surface energy transfer platform

As an important biomarker of malignant tumors, spermine is closely related with some diseases. In this work, a nanometal surface energy transfer (NSET) strategy via the positively charged gold nanorods (AuNRs) and the negatively charged tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) was developed to detect spermine in human urine. Under acidic condition, spermine possessed multi-cationic property and a strong affinity towards the anionic phosphate backbone of calf thymus DNA (ctDNA) by electrostatic attraction as well as the groove binding, which enabled to regulate the process of NSET between AuNRs and TPPS4, leading to the fluorescence quenching of TPPS4. Moreover, the quenched fluorescence was proportional to the concentration of spermine, which was applicable to monitor the level of spermine in human urine in the concentration range of 0.5-7.5 μM. The NSET platform for spemine is simple, selective and time-saving, which has great significance in early cancer diagnosis.

The aggregation induced emission quenching of graphene quantum dots for visualizing the dynamic invasions of cobalt(II) into living cells

A highly sensitive and selective approach for cobalt(ii) detection based on the aggregation induced emission quenching strategy, which is opposite to aggregation induced emission enhancement, was developed using graphene quantum dots (GQDs). The detection could be achieved in the range of 10 nM-5 μM and the limit of detection was 2 nM. Importantly, the as-prepared GQDs showed a specific response to cobalt(ii) with excellent stability in A549 cells owing to their good biocompatibility and long-time anti-photobleaching. Thus, these environmentally and bio-friendly carbon nanomaterials were employed to visualize and monitor significant physiological changes of living cells induced by cobalt(ii). This shows great potential for in vitro analysis of cobalt(ii).