Waste DVD polycarbonate substrate for screen-printed carbon electrode modified with PVP-stabilized AuNPs for continuous free chlorine detection.

An electrochemical free chlorine sensor was developed by modifying a lab-made screen-printed carbon electrode (SPCE) with gold nanoparticles synthesized with polyvinylpyrrolidone (AuNPs-PVP). The electrode was made by screen printing carbon ink on a waste digital versatile disc (SPC-wDVD). PVP was used to stabilize AuNPs. Scanning electron microscopy showed that AuNPs aggregated without the stabilizer. The electrochemical behavior of the SPC-wDVD was evaluated by comparison with commercial SPCEs from two companies. Electrochemical characterization involved cyclic voltammetry and electrochemical impedance spectroscopy. The detection of free chlorine in water samples was continuous, facilitated by a flow-injection system. In the best condition, the developed sensor exhibited linearity from 0.25 to 3.0 and 3.0 to 500 mg L-1. The limit of detection was 0.1 mg L-1. The stability of the sensor enabled the detection of free chlorine at least 475 times with an RSD of 3.2 %. The AuNPs-PVP/SPC-wDVD was able to detect free chlorine in drinking water, tap water and swimming pool water. The agreement between the results obtained with the proposed method and the standard spectrophotometric method confirmed the precision of the developed sensor.

Direct STR typing from human bones.

Identification by STR analysis of bones is time-consuming, mainly due to the lengthy decalcification required and complex DNA extraction process. To streamline this process, we developed a direct STR typing protocol from bone samples. We optimized bone sample amounts using femur and tibia and two commercial PCR kits (Identifiler™ Plus and IDplex Plus kits). Optimally, 100 mg of bone powder in 300 µL PBS buffer was heated at 98 °C for three minutes to produce a supernatant for DNA amplification. IDplex Plus performed better than Identifiler™ Plus in terms of allele recovery and peak height. Fifteen samples of each of seven bone elements (1st distal phalange of hand, capitate, femur, metacarpal 4, patella, talus, and tibia; N = 105) were then subjected to direct STR typing with the optimized protocol, and 94.3% were high partial to full profiles. The performance of the developed protocol was similar for all bone elements. Median peak heights were significantly better in profiles of cancellous bone than compact bone (p = 0.033) and significantly different across the bone elements (p < 0.001). Ten casework samples from various conditions and up to 7-year-PMI were subjected to both direct STR and conventional STR typing. No significant difference in the number of alleles was seen (95% HDI of -13.5 to 5.15). As well as being rapid, convenient, and safe, the protocol could help improve STR typing from bones.