Reversible structural changes in DNA nanomachines have great potential in the field of bioanalysis. Here, we demonstrate an assembly strategy for quencher-free and tunable DNA tweezers based on 2-aminopurine (2-AP), avoiding the tedious fluorescence labelling step. The conformational state of the tweezers could be controlled by specific oligonucleotides (fuel or anti-fuel). Taking advantage of the local environmental sensitivity of 2-AP, the structural changes of the tweezers were easily tracked, and multiple cyclic switching of the tweezers between the open and closed states was achieved. In addition, the influence of oligonucleotide structure on the fluorescence properties of 2-AP was deeply explored. We figured out that the fluorescence of 2-AP was highly quenched by the base-stacking of natural bases in DNA oligonucleotides. Moreover, by comprehensively regulating the type of bases surrounding the inserted 2-AP site, a sensitive fluorescence response towards dynamic change can be obtained. This principle of quencher-free nanodevices based on 2-AP provides a convenient method for monitoring the structural changes of DNA nanomachines.

Near-infrared spectroscopy (NIRS) is often criticized due to its insufficient accuracy in determining body composition compared to the gold standard methods. In this work, we show that the use of multiple source-detector distances, as well as the simultaneous use of physiological and optical features, can significantly improve the accuracy of determination of fat and lean mass percentage in the human body using NIR spectroscopy. The study performed on the n = 292 cohort revealed the mean absolute errors of 3.5% for fat content and 3.3% for soft lean mass percentage prediction (r = 0.93) using the multifrequency bioimpedance analysis (BIA) as a reference. Hence, NIRS can serve as an independent reliable method for body composition analysis with precision close to that of advanced multifrequency BIA.

Novel tetra-2-(biphenyl-4-yl)-1,3-benzoxazol-carboxamide nickel(II) phthalocyanine (NiTBPBXCAPc) and rGO were confirmed using FT-IR, UV-vis, XRD, TGA and Raman spectra. The NiTBPBXCAPc and rGO nanocomposite has been developed to detect hydroquinone (HQN) and chloramphenicol (CPC). NiTBPBXCAPc has been examined using cyclic voltammetry (CV), linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) analysis. The simultaneous CV analysis of HQN and CPC demonstrated the ability of NiTBPBXCAPc@rGO/GCE to execute simultaneous redox reactions. The voltammetric and amperometric limit of detection for HQN and CPC was determined to be 4.5 and 3.5 nM respectively, with a sensitivity of 0.446 and 0.416 μA M-1 cm-2. The amperometric LOD was observed to be 5 and 4 nM with a sensitivity of 0.235 and 0.288 μA M-1 cm-2. Additionally, the NiTBPBXCAPc@rGO/GC electrode is also used for real sample analysis with outstanding recovery. The long-term storage stability, reusability, and real-world sample analysis of the NiTBPBXCAPc@rGO/GC electrode demonstrated its use in environmental analysis.

Direct sulfur-containing compound speciation in crude oils and high-boiling fractions by APCI (+) FT-ICR mass spectrometry

Implantable devices have been widely investigated to improve the treatment of multiple diseases. Even with low drug loadings, these devices can achieve effective delivery and increase patient compliance by minimizing potential side effects, consequently enhancing the quality of life of the patients. Moreover, multi-drug products are emerging in the pharmaceutical field, capable of treating more than one ailment concurrently. Therefore, a simple analytical method is essential for detecting and quantifying different analytes used in formulation development and evaluation. Here, we present, for the first time, an isocratic method for tizanidine hydrochloride (TZ) and lidocaine (LD) loaded into a subcutaneous implant, utilizing reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a UV detector. These implants have the potential to treat muscular spasticity while providing pain relief for several days after implantation. Chromatographic separation of the two drugs was accomplished using a C18 column, with a mobile phase consisting of 0.1% TFA in water and MeOH in a 58 : 42 ratio, flowing at 0.7 ml min-1. The method exhibited specificity and robustness, providing accurate and precise results. It displayed linearity within the range of 0.79 to 100 μg ml-1, with an R2 value of 1 for the simultaneous analysis of TZ and LD. The developed method demonstrated selectivity, offering limits of detection and quantification of 0.16 and 0.49 μg ml-1 for TZ, and 0.30 and 0.93 μg ml-1 for LD, respectively. Furthermore, the solution containing both TZ and LD proved stable under various storage conditions. While this study applied the method to assess an implant device, it has broader applicability for analysing and quantifying the in vitro drug release of TZ and LD from diverse dosage forms in preclinical settings.

Compound-specific isotope analysis (CSIA) via gas chromatography-isotope ratio mass spectrometry (GC-IRMS) is a potent tool to elucidate the fate of (semi-)volatile organic contaminants in technical and environmental systems. Yet, due to the comparatively low sensitivity of IRMS, an enrichment step prior to analysis often is inevitable. A promising approach for fast as well as economic analyte extraction and preconcentration prior to CSIA is dispersive liquid-liquid microextraction (DLLME) - a well-established technique in concentration analysis of contaminants from aqueous samples. Here, we present and evaluate the first DLLME method for GC-IRMS exemplified by the analysis of chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol) as model compounds. The analytes were simultaneously acetylated with acetic anhydride and extracted from the aqueous phase using a binary solvent mixture of acetone and tetrachloroethylene. With this method, reproducible δ13C values were achieved with errors ≤ 0.6‰ (n = 3) for aqueous concentrations down to 100 μg L-1. With preconcentration factors between 130 and 220, the method outperformed conventional liquid-liquid extraction in terms of sample preparation time and resource consumption with comparable reproducibility. Furthermore, we have demonstrated the suitability of the method (i) for the extraction of the analytes from a spiked river water sample and (ii) to quantify kinetic carbon isotope effect for 2,4,6-trichlorophenol during reduction with zero-valent zinc in a laboratory batch experiment. The presented work shows for the first time the potential of DLLME for analyte enrichment prior to CSIA and paves the way for further developments, such as the extraction of other compounds or scaling up to larger sample volumes.

In this work, a microfluidic paper-based analytical device (μPAD) was developed to detect the biopesticide azadirachtin (Aza) through a colorimetric assay. High precision estimation of Aza is classically carried out using high performance liquid chromatography (HPLC), which requires highly skilled personnel. Acidified vanillin is a commonly used colorimetric indicator in thin layer chromatography for detection of various phytochemicals. However, the assay involves concentrated acid, which limits the choice of paper substrates for paper-based sensors and raises safety concerns. In this work, we show how the assay can be extended from the liquid phase to a paper substrate. Glass microfiber (GMF) filter paper was found to be suitable paper as it was acid resistant; besides, its hydrophilicity enabled smooth flow of reagents. A microfluidic paper-based sensor (μPAD) was developed by sandwiching 5 mm sized GMF dots between two parafilm sheets. We demonstrate the use of colorimetric assay on the μPAD for on-site detection of Aza in neem kernels. The magenta color developed upon the reaction of acidified vanillin with Aza was captured using a smart-phone and analysed using RGB levels in the image. Calibration was established using neem kernel extract of known concentration. Linearity was seen in the concentration range of 5 to 25 mg L-1 Aza. A limit of detection of 2.3 mg L-1 was obtained using this method. The colorimetric assay showed a relative recovery of >85% when compared with the values obtained from HPLC. The stability of the reagents on the GMF sensor was investigated to understand the storage conditions and shelf life of the reagents and sensor. The present work demonstrates the development of a portable sensor for on-site detection of phytochemicals that can be an integral part of the agricultural supply chain.

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