The authors report on a simple strategy for sensitive determination of the activity of terminal deoxynucleotidyl transferase (TdT) using copper nanoclusters (CuNCs) as fluorescent probes. TdT-polymerized long chain AT-rich DNA serves as a template for the synthesis of the CuNCs, and TdT activity is detected fluorometrically at excitation/emission wavelengths of 340/570 nm. The protocol relies on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs. The calibration plot is linear in the 0.7 to 14 U L?1 activity range, with a 60 mU L?1 detection limit (at a signal-to-noise ratio of 3). The protocol was applied to determine TdT activity in acute lymphatic leukemia cells. This approach is selective, simple, convenient and cost-efficient because a complex DNA sequence is not required. In our perception, the method provides a viable new platform for monitoring the activity and inhibition of TdT.
Graphical abstract Based on the target-triggered formation of dsDNA polymers and in-situ formation of CuNCs with strong fluorescence, a turn-on fluorescence assay for TdT activity is presented.
The authors describe a method for the differentiation of penicillamine (PA) enantiomers by using CdSe/ZnS quantum dots (QDs) modified with β-cylodextrin (β-CD-CdSe/ZnS QDs). Selective enantiorecognition of L-PA and D-PA was accomplished by virtue of selective host-guest interaction between the PAs and the β-CD pockets on the QDs. The fluorescence intensity of the modified QDs decreases in the presence of L-PA. On the contrary, it increases in the presence of D-PA. These findings form the basis for a new method for recognition of PA enantiomers. Under optimized conditions, a linear relationship exists between fluorescence intensity and D-PA concentration in the 0.1 to 5.0 mg L?1 range, and between 0.8 and 5.0 mg L?1 for L-PA. Detection limits are 0.06 mg L?1 for D-PA, and 0.2 mg L?1 for L-PA. The potential of this method has been demonstrated by the determination of D-PA in pharmaceutical formulations and L-PA in (spiked) environmental samples.
Graphical abstract Selective and specific enantiorecognition of penicillamine (PA) enantiomers using β-cylodextrin modified CdSe/ZnS quantum dots is described. Fluorescence intensity increases in the presence of D-PA, but it decreases in the presence of L-PA. Results were the basis for analytical applications.
The authors report on a surface molecular imprinting strategy for synthesizing magnetic and molecularly imprinted core-shell polymer nanoparticles (MMIPs) with a typical size of 320 nm. The triazophos-imprinted polymer shell on 180-nm magnetite particles (modified with 3-methacryloxypropyl trimethoxysilane) was obtained by radical polymerization of ethylene glycol dimethacrylate in the presence of triazophos, this followed by extractive removal of triazophos. The resulting MMIPs possess large binding capacity, high recognition selectivity, and fast binding kinetics for triazophos. They can be easily separated from a solution by using a magnet. These features result in a convenient and selective solid-phase extraction procedure for triazophos prior to its determination by UV spectrometry or by GC analysis. The method was successfully applied to the extraction and clean-up of triazophos residues in spiked homogenates of vegetables with recoveries in the range of 89.2 ~ 99.0%. The detection limits for triazophos by the UV assay and GC assay are 0.93 nM and 0.32 nM, respectively.
Graphical abstract The core-shell magnetic molecularly imprinted polymer nanoparticles (MMIPs) with a nanoscale triazophos-imprinted polymer shell were prepared by surface imprinting onto the surfaces of 3-methacryloxypropyl trimethoxysilane (MATS) modified Fe3O4 magnetic nanoparticles. They were successfully applied for the extraction and clean-up of ultra trace triazophos residues in spiked homogenates of vegetable samples. MMIPs exhibit the larger binding capacity, faster binding kinetics, higher recognition selectivity, good reusability and stability, and excellent magnetic responses.
The authors report on a robust method for the synthesis of gold nanorods (AuNRs) with tunable dimensions and longitudinal surface plasmon resonance. The method relies on seed-mediated particle growth in the presence of benzalkonium chloride (BAC) in place of the widely used surfactant cetyltrimethyl ammonium bromide (CTAB). Uniform AuNRs were obtained by particle growth in solution, and BAC is found to stabilize the AuNRs for >1 year. The SERS activity of the resulting AuNRs is essentially identical to that of CTAB-protected nanorods. The SERS activity of the BAC protected nanorods was applied to the quantitative analysis of potato virus X (PVX). The calibration plot for PVX is linear in the 10 to 750 ng?mL?1 concentration range, and the detection limit is 2.2 ng?mL?1.
Graphical abstract SERS-active gold nanorods (AuNRs) have been prepared by using benzalkonium chloride as stabilization agent. Effects of chemical parameters on AuNRs have been explored and AuNRs were used in quantitative analysis of potato virus X (PVX).
The paper reports on a method for the detection of nanocellulose (NC) in consumer products by making use of a combination of (a) liquid-liquid extraction with an ionic liquid, and (b) size characterization by asymmetric flow field-flow fractionation (AF4) coupled to multi-angle light scattering (MALS) and refractive index (RI) detection. Both AF4 and MALS are viable tools for characterizing the size of the nanofibers. Sample preparation is easy, and the extraction efficiency of the method is 80.9 ± 1.8% (n = 5). It was applied to the detection of NC in toothpaste and coconut foodstuff to verify the practicability of the method.
Graphical abstract Nanocellulose (NC) monitoring from coconut products and toothpaste and its size characterization by liquid-liquid extraction and asymmetric flow field-flow fractionation equipped with multi-angle light scattering and refractive index detection (AF4-MALS-RI).
Carbon polymer dots (CPDs) were prepared by a one-pot aqueous synthetic route from ascorbic acid and diethylenetriamine at room-temperature. The CPDs under 350-nm excitation exhibit blue fluorescence peaking at 430 nm with a quantum yield of 47%. Other features include an average diameter of 5 nm, a fluorescence that is independent of the excitation wavelength, good water dispersibility and photostability, and excellent biocompatibility. The CPDs are shown to be viable fluorescent probes for ferric ion which acts as a strong quencher. The response to Fe(III) is linear in the 0.2 to 10 μM concentration range, and the detection limit is 0.1 μM. The probe was applied to the determination of Fe(III) in environmental waters and to intracellular imaging of ferric ions in HeLa cells.
Graphical abstract Carbon polymer dots (CPDs) are prepared from ascorbic acid and diethylenetriamine (DETA) at room-temperature (RT). The RT-CPDs exhibit excellent optical performance, biocompatibility and selectivity of quenching by ferric ions. This can be applied for determination and intracellular imaging of ferric ion.
Hydrothermal treatment of a mixture of ethylene diamine, phosphoric acid and citric acid under ambient pressure generates fluorescent carbon dots that are co-doped with phosphorus and nitrogen. These have features such as (a) both green fluorescence (peaking at 430 nm; 30% quantum yield) and red fluorescence (peaking at 500 nm, quantum yield 78%), (b) wavelength-dependent emission peaks, and (c) insensitivity to changes of pH values, dot concentration and ionic strength. The C-dots are useful for both fluorescent (FL) and photoacoustic (PA) imaging of living tissue. PA imaging warrants better spatial resolution and allows deeper tissues to be imaged compared to most optical imaging techniques. It is essential to assign a photoacoustic contrast agent as most of the diseases do not show a natural photoacoustic contrast in their early stage. The dually emitting C-dots are shown to be a useful contrast agent for PA and FL imaging of mice tumors. Intravenous administration of the C-dots resulted in strong signals in both PA and FL imaging.
Graphical abstract Photographs of the excitation wavelength-dependent fluorescence of P,N-doped C-dots obtained from ethylenediamine, phosphoric acid and citric acid. Intravenous administration of the C-dots resulted in strong signals in both photoacoustic (PA) and fluorescent (FL) imaging.
