Search Results (7)

The toxic effects of antimony pose risks to human health. Therefore, simple analytical techniques for its widescale monitoring in water sources are in demand. In this study, a sensitive microplate apta-enzyme assay for Sb³⁺ detection was developed. The biotinylated aptamer A₁₀ was hybridized with its complementary biotinylated oligonucleotide T₁₀ and then immobilized on the surface of polysterene microplate wells. Streptavidin labeled with horseradish peroxidase (HRP) bound to the biotin of a complementary complex and transformed the 3,3′,5,5′-tetramethylbenzidine substrate, generating an optical signal. Sb³⁺ presenting in the sample bounded to an A₁₀ aptamer, thus releasing T₁₀, preventing streptavidin-HRP binding and, as a result, reducing the optical signal. This effect allowed for the detection of Sb³⁺ with a working range from 0.09 to 2.3 µg/mL and detection limit of 42 ng/mL. It was established that the presence of Ag⁺ at the stage of A₁₀/T₁₀ complex formation promoted dehybridization of the aptamer A₁₀ and the formation of the A₁₀/Sb³⁺ complex. The working range of the Ag⁺-enhanced microplate apta-enzyme assay for Sb³⁺ was determined to be 8–135 ng/mL, with a detection limit of 1.9 ng/mL. The proposed enhanced approach demonstrated excellent selectivity against other cations/anions, and its practical applicability was confirmed through an analysis of drinking and spring water samples with recoveries of Sb³⁺ in the range of 109.0–126.2% and 99.6–106.1%, respectively. Full article

While fluorescent sensors have been developed for monitoring metal ions in health and diseases, they are limited by the requirement of an excitation light source that can lead to photobleaching and a high autofluorescence background. To address these issues, bioluminescence resonance energy transfer (BRET)-based protein or small molecule sensors have been developed; however, most of them are not highly selective nor generalizable to different metal ions. Taking advantage of the high selectivity and generalizability of DNAzymes, we report herein DNAzyme-based ratiometric sensors for Zn²⁺ based on BRET. The 8-17 DNAzyme was labeled with luciferase and Cy3. The proximity between luciferase and Cy3 permitted BRET when coelenterazine, the substrate for luciferase, was introduced. Adding samples containing Zn²⁺ resulted in a cleavage of the substrate strand, causing dehybridization of the DNAzyme construct, thus increasing the distance between Cy3 and luciferase and changing the BRET signals. Using these sensors, we detected Zn²⁺ in serum samples and achieved Zn²⁺ detection with a smartphone camera. Moreover, since the BRET pair is not the component that determines the selectivity of the sensors, this sensing platform has the potential to be adapted for the detection of other metal ions with other metal-dependent DNAzymes. Full article

In this work, the contribution of different types of carbon blacks (N115, N330, N550, N660) and their primary and secondary thermally cracked recovered carbon blacks to the mechanical properties of NR composites was evaluated. The thermally cracked recovered carbon blacks were prepared by cracking the rubber composites at 500 °C and de-hybridizing them at 900 °C. The characterization of the thermally cracked recovered carbon blacks by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that carbon blacks after primary and secondary thermal cracking recovery were more prone to aggregation and exhibited a higher degree of carbon defects. The number and type of functional groups on the surface of these carbon blacks were significantly reduced. For NR composites with pristine samples added, the mechanical properties and the bound rubber content tests showed that the mechanical properties of the NR composites became weaker with the increase in carbon black particle size. The bound rubber content also decreased with increased carbon black particle size. The mechanical properties of the NR composites reinforced with carbon black recovered by primary and secondary thermal cracking would therefore decrease. The results of AFM and DSC tests further confirmed the decreasing trend of bound rubber. The present work demonstrates the effect of bound rubber content variation on the mechanical properties of rubber, demonstrates the morphology of bound rubber more visually, and provides new insights into the reinforcement theory of CB. Full article

The optimal development of biosensors is a costly and time-consuming task, since an enormous amount of experiments is required. Therefore, the possibility of reusing the biosensors is highly desirable. In this work, a protocol based on the use of formamide for the regeneration of nanophotonic biosensors used for oligonucleotides detection is presented. This protocol was carried out online using the microfluidic system used to drive the target samples to the nanophotonic biosensor, thus allowing the possibility of running several experiments in a row using the same biosensor. Full article

The intramolecular fluorescence self-quenching phenomenon is a major drawback in developing high-performance fluorometric biosensors which use common fluorophores as signal generators. We propose two strategies involving liberation of the fluorescent molecules by means of enzymatic fragmentation of protein or dehybridization of double-stranded DNA. In the former, bovine serum albumin (BSA) was coupled with the fluorescent BODIPY dye (Red BSA), and then immobilized on a solid surface. When the insolubilized Red BSA was treated with proteinase K (10 units/mL) for 30 min, the fluorescent signal was significantly increased (3.5-fold) compared to the untreated control. In the second case, fluorophore-tagged DNA probes were linked to gold nanoparticles by hybridization with capture DNA strands densely immobilized on the surface. The quenched fluorescence signal was recovered (3.7-fold) by thermal dehybridization, which was induced with light of a specific wavelength (e.g., 530 nm) for less than 1 min. We next applied the Red BSA self-quenching relaxation technique employing enzymatic fragmentation to a high-performance immunoassay of cardiac troponin I (cTnI) in a microtiter plate format. The detection limit was 0.19 ng/mL cTnI, and the fluorescent signal was enhanced approximately 4.1-fold compared with the conventional method of direct measurement of the fluorescent signal from a non-fragmented fluorophore-labeled antibody. Full article

We here report a rapid, sensitive, selective and label-free fluorescence detection method for cysteine (Cys). The conformation of mercury-specific DNA (MSD) changes from a random coil form to a hairpin structure in the presence of Hg²⁺ due to the formation of a thymine-Hg²⁺-thymine (T-Hg²⁺-T) complex. Cys can selectively coordinate with Hg²⁺ and extract it from the thymine-Hg²⁺-thymine complex. The hairpin structure dehybridizes and the fluorescence intensity of Sybr Green I (SG) decreases upon addition of Cys because SG efficiently discriminates mercury-specific DNA and mercury-specific DNA/Hg²⁺ complex. The detection can be finished within 5 min with high sensitivity and selectivity. In addition, we can obtain variable dynamic ranges for Cys by changing the concentration of MSD/Hg²⁺. Full article

It is well known that non-enzymatic template directed molecular replicators X + nO -> 2X exhibit parabolic growth d[X]/dt -> k[X]^1/2. Here, we analyze the dependence of the effective replication rate constant k on hybridization energies, temperature, strand length, and sequence composition. First we derive analytical criteria for the replication rate k based on simple thermodynamic arguments. Second we present a Brownian dynamics model for oligonucleotides that allows us to simulate their diffusion and hybridization behavior. The simulation is used to generate and analyze the effect of strand length, temperature, and to some extent sequence composition, on the hybridization rates and the resulting optimal overall rate constant k. Combining the two approaches allows us to semi-analytically depict a replication rate landscape for template directed replicators. The results indicate a clear replication advantage for longer strands at lower temperatures in the regime where the ligation rate is rate limiting. Further the results indicate the existence of an optimal replication rate at the boundary between the two regimes where the ligation rate and the dehybridization rates are rate limiting. Full article