Yijuan Long

Study on the fluorescence characteristics of carbon dots.

Herein, we prepared water-soluble fluorescent carbon dots with diameter about 1.5 nm from cheap commercial lampblack. These fluorescent carbon nanoparticles are stable toward photobleaching and stable in water for more than half a year without fluorescence decrease. In order to improve its fluorescence properties, we passivated these nanoparticles with bisamino-terminated polyethylene glycol (PEG(1500 N)). Therefore, both fluorescence quantum yield and lifetime increased after this progress. In addition, the passivated carbon dots were more inert to solvent than the bare one and showed different responses to pH change.

CdTe quantum dots as a highly selective probe for prion protein detection: colorimetric qualitative, semi-quantitative and quantitative detection.

CdTe quantum dots (QDs) were used as a highly selective probe for the detection of prion protein. Orange-emitting precipitates appeared within 30s of the addition of recombination prion protein (rPrP) to a solution of green-emitting CdTe QDs. This allowed colorimetric qualitative and semi-quantitative detection of rPrP. The decrease in fluorescence intensity of the supernatant could be used for quantitative detection of rPrP. The fluorescence intensity of the supernatant was inversely proportional to the rPrP concentration from 8 to 200 nmol L(-1) (R(2)=0.9897). Transmission electron microscopy results showed that fibrils existed in the precipitates and these were partly transformed to amyloid plaques after the addition of rPrP.

An aptamer-functionalized gold nanoparticle biosensor for the detection of prion protein

Prions are a special class of pathogens that cause a number of fatal neurodegenerative diseases in mammals. This paper presents a very simple and convenient biosensor for detecting prion protein, in which a prion protein aptamer was used as the molecular recognition group and gold nanoparticles were used as the signal report group. Binding of the target molecular prion protein resulted in the enhancement of resonance light scattering (RLS) by the gold nanoparticles. A linear relationship was then identified between the enhanced RLS intensity and the concentration of prion protein in the range 0.2 to 50 nmol L−1, with a limit of detection of 0.07 nmol L−1 (3σ). The biosensor has very good selectivity for prion protein without interference by coexisting proteins, amino acids or metal ions. This “aptasensor” offers a rapid, selective and sensitive route for prion protein detection and has good potential for use in practical applications.

Dichlorofluorescein as a peroxidase mimic and its application to glucose detection

Herein, we discovered, for the first time, that 2′,7′-dichlorofluorescein (DCF), as a novel peroxidase mimic, can catalyze the oxidation of the classical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, producing a colour reaction. Although a variety of peroxidase mimics have been actively developed recently, few studies have been focused on the small molecule peroxidase mimics. As a novel peroxidase mimic, DCF was verified to be highly stable, well reproducible and of low cost, exhibiting typical Michaelis–Menten kinetics and a strong affinity towards H2O2 and TMB. On the basis of these findings, we further demonstrated the novel use of DCF for easy and simple detection of H2O2 and glucose. This type of new small molecule peroxidase mimic is expected to be used in medical clinical diagnosis, and this novel finding not only further confirms the peroxidase activity of small molecules of fluorescein derivatives, but also opens new opportunities to deepen the knowledge of this new class of small molecule enzymes.

A sandwich immunoassay for detection of Aβ1-42 based on quantum dots

Alzheimers disease (AD) is the primary cause of dementia over the age of 60, affecting more than 35 million people worldwide. Methods for early diagnosis of AD are critical for the development of effective treatments to combat this debilitating disease. It was confirmed that amyloid-beta peptide 1-42 (Aβ(1-42)) is the biomarker of its early diagnosis. In this work, we present a new sandwich immunoassay method for the detection of Aβ(1-42) based on quantum dot (QDs) nanolabels and magnetic separation. In the presence of Aβ(1-42), QDs linked to magnetic beads (MB) via the formation of immune-sandwich complex and can be removed by a magnetic field. And as a result, fluorescence intensity from QDs in the supernatant decreased. Under the optimized conditions, there is a linear relationship between the fluorescence intensity of supernatant solution and the concentration of Aβ(1-42) from 0.50 to 8.0 nM with a limit detection of 0.2 nM (3σ). This immunoassay was applied to detect Aβ(1-42) in human cerebrospinal fluid (CSF) successfully.

Intrinsic Peroxidase-like Activity of Ficin

Ficin is classified as a sulfhydryl protease isolated from the latex of fig trees. In most cases, a particular enzyme fits a few types of substrate and catalyzes one type of reaction. In this investigation, we found sufficient proofs for the intrinsic peroxidase-like activity of ficin and designed experiments to examine its effectiveness in a variety of scenarios. Ficin can transform peroxidase substrates to colored products in the existence of H2O2. Our results also indicate that the active sites of peroxidase-like activity of ficin are different from that of protease, which reveals that one enzyme may catalyze more than one kind of substrate to perform different types of reactions. On the basis of these findings, H2O2 releasing from MCF-7 cells was detected successfully. Our findings support a wider application of ficin in biochemistry and open up the possibility of utilizing ficin as enzymatic mimics in biotechnology and environmental monitoring.

Visual detection of prion protein based on color complementarity principle

Two complementary colors mixed in a proper proportion will produce a neutral color in the color theory. A novel colorimetric method on basis of the color complementarity principle has been well-established to detect recombinant prion protein (rPrP). We found that a colorless solution appeared after mixing orange CdTe quantum dots (QDs) with green-blue malachite green (MG) because of color complementarity. After the addition of rPrP into the mixed solution, the color changed from colorless to green-blue because rPrP could induce the aggregation of QDs, rapidly. And it could be observed by naked eyes. Based on this phenomenon, we developed a simple assay for visual detection of rPrP. At the same time, we obtained excellent correlation between absorption and concentrations of rPrP from 1 nmol L(-1) to 78 nmol L(-1) with the limit of detection of 0.3 nmol L(-1) (3σ). Moreover, it can be applied to determine rPrP in human serum successfully. Importantly, this assay possesses the advantages of simplicity, rapidity, sensitivity, and selectivity, and shows the potential in the clinical diagnostic test of early prion disease and provides the possibility of preventing the spread of prion diseases.

Constructing H+-triggered bubble generating nano-drug delivery systems using bicarbonate and carbonate

Nanoparticles have the great potential to act as drug delivery carriers, and such systems must effectively deliver the drug to the cancer cells, and provide intracellular drug release. In this research, two types of H+-triggered bubble generating nanosystems (BGNS) were developed which were obtained using hollow mesoporous silica nanoparticles loaded with doxorubicin and subsequently treated with bubble generating agents, i.e., sodium bicarbonate (SBC) and ammonium carbonate (AC). These were named BGNS-SBC and BGNS-AC. After internalization by the tumor cells, the H+ reacts with bicarbonate or carbonate to generate carbon dioxide bubbles quickly in an acidic environment of endo/lysosomes, which results in lysosomal membrane permeabilization (LMP). Then, the enhanced LMP induced cancer cell death by an apoptosis-like pathway because of the release of caspase-3 from the lysosome into the cytoplasm. In addition, BGNS-SBC and BGNS-AC possessed remarkable cytotoxicity against MCF-7 cells and efficiently overcame the multidrug resistance (MDR) of MCF-7/adriamycin cells. Therefore, these bubble generating nanosystems could be a promising nanocarrier for the treatment of tumors.

Rapid size-dependent separation of CdTe quantum dots with prion protein

Prion proteins (PrP) were successfully used to separate CdTe quantum dots (QDs) of different size based on the size-dependent aggregation. Even though the size disparity was only 0.8–2 nm, red-, yellow- and green-emitting QDs could be separated from one another by addition of different concentrations of PrP. This novel separation method allows controllable, rapid and simple separation of QDs without requiring large amounts of expensive reagents and complicated technology, which can be developed into a versatile method for separating diversiform nanoparticles.

The effect of quantum dot labeling on virus activity

In order to evaluate the effect of quantum dot (QD) labeling on virus activity, cell viability and cytokine secretion were measured after host cells were infected by QD-labeled H9N2 and unlabeled H9N2. Our results suggested that in the process of QD labeling, biotin modification (<1 mg mL−1) had no obvious effect on virus activity. However, follow-up QD labeling enhanced the virus toxicity toward host cells and caused a high level of cytokine secretion. And our results indicate that QD-labeling is not suitable for long time tracing of viruses.