Effect of osmotic dehydration combined with vacuum freeze-drying treatment on characteristic aroma components of peach slices.

Hot air drying (HD), vacuum freeze drying (FD), and pilot-scale freeze drying (PSFD) are extensively used to prepare peach slices. However, the aroma of hot air drying and vacuum freeze-drying is yet to be addressed. In this study, HS-SPME-GC-MS was used to characterize and quantify the volatile compounds in peach slices. First, 33, 36, and 46 volatile compounds were identified and quantified in the HD, FD, and PSFD groups, respectively. PSFD is preferable to HD and FD in terms of the volatile compound types, content, and aroma profiles. PSFD was selected for subsequent permeation and dehydration experiments. The key aroma compounds with an OAV ≥ 1 were found in the PSFD30 group. GC-O analysis was conducted on the PSFD30 group, leading to the preliminary identification of 2-methylbutanal, pentanal, hexanal, 2-hexenal, phenylacetaldehyde, ethyl acetate, 2-methylbutyl acetate, ethyl lactate, linalool, methyl heptenone, and γ-octalactone as distinctive aromas in dried peach slices.

Highly-efficient peroxidase-like catalytic activity of graphene dots for biosensing.

In recent years, considerable efforts have been devoted to the construction of efficient enzyme mimetics, which have significant advantages of simple synthesis, good stability and design flexibility. In this paper, we described that graphene dots (GDs) possess highly-efficient peroxidase-like catalytic activity, and its activity is much higher than graphene oxide (GO) with large size. They can catalyze the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue product, which can be used for H2O2 detection by measuring the absorbance change. This catalytic reaction can be also used for other analyte detection by monitoring the generation or consumption of H2O2, such as glucose and reduced glutathione (GSH). The GDs-based system permits detection of as low as 10nM H2O2, which is much lower than that of other nanomaterials-catalyzed methods. Meanwhile, the detection limit of this system is 0.5 µM for glucose and 0.5 µM for GSH, respectively. Furthermore, the proposed system also shows high selectivity and is capable of sensing in complicated biological samples such as cell lysate. Due to their high catalytic activity, high diffusion and excellent biocompatibility, GDs can be expected to be applied in various fields, such as biotechnology, medical diagnostics and environmental monitoring.

Enzyme-free fluorescence aptasensor for amplification detection of human thrombin via target-catalyzed hairpin assembly.

Aptamers have many advantages, such as simple synthesis, good stability, high binding affinity and wide applicability, making them suitable candidates for protein detection. Since the disease-related protein may be present in very small amounts in biological samples, the development of amplification paths for aptasensors is essential. In this paper, we develop a simple and enzyme-free amplified aptasensor for protein detection via target-catalyzed hairpin assembly. This aptasensor contains two DNA hairpins termed as H1 and H2. H1, which is modified at its 5' and 3' ends with a fluorophore and a quencher respectively, consists of the aptamer sequence of human thrombin. Meanwhile, H2 is partially complementary to H1. These two hairpins H1 and H2 interact slowly with each other. Upon the addition of target protein, it can facilitate the opening of the hairpin structure of H1 and thus accelerate the hybridization between H1 and H2, resulting in the significant fluorescence enhancement of the system. By monitoring the change in fluorescence intensity, we could detect the target protein with high sensitivity. The detection limit of this aptasensor is 20 pM, which is more than two orders of magnitude lower than that of reported unamplified aptasensors. Furthermore, this amplified aptasensor shows high selectivity toward its target protein. Thus, the proposed aptasensor could be used as a simple, sensitive and selective platform for target protein detection.

Enzyme-free signal amplification in the DNAzyme sensor via target-catalyzed hairpin assembly.

A simple, highly sensitive and enzyme-free DNAzyme sensor based on target-catalyzed hairpin assembly is developed, which permits detection of 0.1 pM target DNA. Furthermore, this DNAzyme sensor is capable of detecting target DNA in real samples because of its high selectivity.

Nicking enzyme based homogeneous aptasensors for amplification detection of protein.

A simple and highly sensitive homogeneous aptasensor is developed, which relies on nicking enzyme. The sensitivity of this newly proposed aptasensor is about three orders of magnitude higher than that of traditional homogeneous aptasensors. Furthermore, it is capable of detecting target protein in real samples.