Yalei Hu

Nitrogen-doped Carbon Dots Mediated Fluorescent on-off Assay for Rapid and Highly Sensitive Pyrophosphate and Alkaline Phosphatase Detection

In this report, a novel fluorescent sensing platform using nitrogen-doped carbon dots (N-CDs) as probes for fluorescence signal transmission has been designed for the detection of significant biomolecules pyrophosphate (PPi) and alkaline phosphatase (ALP). The high fluorescent N-CDs could be selectively quenched by Cu2+, and recovered by the addition of PPi because PPi preferentially binds to Cu2+. Once ALP was introduced into the system, ALP can specifically hydrolyze PPi into Pi, the intense fluorescence of N-CDs could be quenched again due to the recombination of the as-released Cu2+ with N-CDs. So, fluorescence of N-CDs is regulated by an ALP-triggered reaction. Based on this strategy, we demonstrated that N-CDs could serve as a very effective fluorescent sensing platform for label-free, sensitive and selective detection of PPi and ALP with low detection limit of 0.16 μM and 0.4 U/L for PPi and ALP, respectively. Moreover, the assay time is just around 0.5 min for PPi and 30 min for ALP. This developed strategy shows remarkable advantages including sensitive, rapid, simple, convenient, and low-cost and so forth. Furthermore, this method was also successfully applied to monitor ALP in human serum, which indicates its great potential for practical applications in biological and clinical diagnosis.

A novel label-free fluorescent molecular beacon for the detection of 3′–5′ exonuclease enzymatic activity using DNA-templated copper nanoclusters

The 3′–5′ exonuclease plays key roles in maintaining genome stability; therefore, the detection of 3′–5′ exonuclease activity is very important for disease diagnosis and drug development. In this study, we present a novel highly sensitive and label-free fluorescent assay to detect the activity of exonuclease III (Exo III) using molecular beacon DNA with a polythymine (T) loop as a template for the formation of fluorescent copper nanoparticles (CuNPs). Upon the addition of Exo III, the molecular beacon probe was digested into mono- or short oligonucleotides by the exonucleases and failed to form fluorescent CuNPs. As a result, the fluorescence intensity of CuNPs decreased. This method exhibited a very low detection limit of 0.02 U mL−1 for Exo III. The designed molecular beacon probe can be a potential label-free strategy for the detection of other nuclease activity.

Synthesis of Luminescent Carbon Dots with Ultrahigh Quantum Yield and Inherent Folate Receptor-Positive Cancer Cell Targetability

Carbon dots (CDs) have a wide range of applications in chemical, physical and biomedical research fields. We are particularly interested in the use of CDs as fluorescence nanomaterials for targeted tumor cell imaging. One of the important aspects of success is to enhance the fluorescence quantum yields (QY) of CDs as well as increase their targetability to tumor cells. However, most of the reported CDs are limited by relative low QY. In the current study, for the first time, one-step synthesis of highly luminescent CDs by using folic acid (FA) as single precursor was obtained in natural water through hydrothermal method. The as-prepared CDs exhibited QY as high as 94.5% in water, which is even higher than most of organic fluorescent dyes. The obtained CDs showed excellent photoluminescent activity, high photostability and favorable biocompatibility. The FA residuals in CDs led to extraordinary targetability to cancer cells and promoted folate receptor-mediated cellular uptake successfully, which holds a great potential in biological and bioimaging studies.

A label-free aptasensor for highly sensitive ATP detection by using exonuclease I and oligonucleotide-templated fluorescent copper nanoparticles

In this work, we developed a simple and highly sensitive fluorescence method for the determination of ATP based on a designed multifunctional oligonucleotide, which holds the ability of synthesizing fluorescent copper nanoparticles (CuNPs) as well as recognizing ATP molecules. In the absence of ATP, this multifunctional probe containing an ATP aptamer and poly T strand can be digested upon the addition of Exo I, which leads to the failure of synthesizing poly T-templated fluorescent CuNPs, whereas in the presence of ATP, the ATP aptamer folds into a G-quadruplex structure, which makes it resistant to digestion by Exo I. Accordingly, the poly T strand is reserved and can be used as an efficient template for the formation of CuNPs with strong fluorescence. Thus, the concentration of ATP could be identified very easily by observing fluorescence changes of this sensing system. This signal-on assay exhibits high sensitivity to ATP with a detection limit of 500 nM in the range of 1–80 μM. Further specificity investigation and real sample anti-interference experiments show that this assay also has high selectivity and anti-interference ability.

A rapid and sensitive turn-on fluorescent probe for ascorbic acid detection based on carbon dots–MnO2 nanocomposites

Ascorbic acid (AA) is a significant small biomolecule and plays a key role in many biochemical processes. In this work, a rapid turn-on fluorescent probe was developed for sensitive and selective sensing of AA based on carbon dots–MnO2 nanocomposites. The nanocomposites were constructed by in situ synthesis of MnO2 nanosheets in carbon dot (C-dot) solution, and the fluorescence of C-dots was quenched with the formation of the nanocomposites due to the fluorescence resonance energy transfer (FRET) from C-dots to the generated MnO2 nanosheets. Once AA was introduced into the system, MnO2 nanosheets were reduced to Mn2+ and the fluorescence of C-dots would be recovered. Under the optimized conditions, this method shows rapid and sensitive response toward AA, the assay time is 2 min and the limit of detection is 68 nM. Moreover, the carbon dots–MnO2 nanocomposite based fluorescence sensing system was successfully employed to determine AA in commercial tablets with satisfactory results. Taking full advantage of C-dots and MnO2 nanosheets, this probe shows remarkable properties including easy operation, low cost and good biocompatibility, and has great potential to be used in biological and clinical diagnostic applications.

A facile fluorescence assay for rapid and sensitive detection of uric acid based on carbon dots and MnO2 nanosheets

Uric acid (UA) is an important biological molecule in human pathology and is related to many critical diseases. Designing a simple and rapid method for sensitive UA determination is of great significance. Herein, we report a novel turn-on fluorescence assay for UA detection, based on fluorescence resonance energy transfer (FRET) between carbon dots (C-dots) and MnO2 nanosheets. MnO2 nanosheets can adsorb C-dots to form nanocomposites, where the fluorescence of C-dots is quenched via FRET. Fluorescence recovered when UA was introduced into the sensing system due to the decomposition of MnO2 nanosheets to Mn2+. Under optimized conditions, the fluorescence signal was linearly related to UA concentration in the range of 0.1–200 μM and the detection limit was as low as 45 nM. Moreover, this developed assay was successfully applied for human urine sample analysis, which indicated that this strategy could be an efficient tool for clinical disease diagnosis.

One-Pot Green Synthesis of Ultrabright N-Doped Fluorescent Silicon Nanoparticles for Cellular Imaging by Using Ethylenediaminetetraacetic Acid Disodium Salt as an Effective Reductant

Because of excellent photoluminescence properties, robust chemical inertness, and low cytotoxicity of silicon nanoparticles (Si NPs), exploration of their applications in bioimaging is of great interest. Up to date, a method to synthesis Si NPs with high fluorescence quantum yield (QY) is still challenging. This situation limits the further applications of Si NPs. In this work, we report a mild, simple, and green one-pot method to synthesis N-doped fluorescent Si NPs with an ultrahigh QY up to 62%, using ethylenediaminetetraacetic acid disodium salt as an effective reductant. The obtained ultrabright Si NPs have properties such as relative small size (about 2 nm), water dispersibility, robust stability, and biocompatibility. The as-prepared Si NPs were further applied for cellular imaging with satisfactory results, indicating their great potential in bioimaging applications.