Quantifying visible absorbance changes and DNA degradation in aging bloodstains under extreme temperatures

Physicochemical property changes observed in a degrading bloodstain can be used to estimate its time since deposition (TSD) and provide a timestamp to the sample's age. Many of the time-dependent processes that occur as a bloodstain degrades, such as DNA fragmentation and changes in hemoglobin structure, also exhibit temperature-dependent behaviours. Previous studies have demonstrated that pairing high-resolution automated gel electrophoresis and visible absorbance spectroscopy could be used to quantify the rate of degradation of a bloodstain in relation to time and storage substrate. Our study investigates such trends with an added factor, extreme temperatures. Passive drip stains were stored in either microcentrifuge tubes or on FTA cards at either -20°C, 21°C or 40°C and tested over 11 time points spanning 15 days. For both storage substrates, the wavelength at maximum absorbance for the Soret band and the maximum absorbance of the Alpha band showed a negative trend over time suggesting that spectral shifts are informative for TSD estimates. The ratio of the maximum peak height for DNA fragments lengths of 500-1000 base pairs to 1000-5000 base pairs was the most informative DNA variable in relation to time for both substrates. Cross-validation suggested the appropriate fit of the models with the data and reasonable predictive ability. We integrated both DNA concentration and hemoglobin visible absorbance metrics using principal component analysis (PCA) into a single model. Adding the random effect of the donor to the PCA model accounted for a large portion of the variation as did storage method and temperature. Additionally, canonical correspondence showed that temperature corresponded differently to the response variables for FTA card and microcentrifuge tube samples, suggesting a substrate specific effect. This study confirms that pairing DNA concentration and hemoglobin's visible absorbance can provide insight on the effect of different environmental and storage conditions on bloodstain degradation. While the level of uncertainty surrounding TSD estimates still precludes its use in the field, this study provides a valuable framework that improves our understanding of variation surrounding TSD estimates, which will be critical to any eventual application.

Layer-By-Layer Film Engineering for Sequential Gene Delivery

Layer-by-layer (LbL) films are assembled with poly(amido amine)s (PAAs), a type of polycations containing bioreducible disulfide bond, and DNA plasmids to enable LbL film degradation in physiologic conditions by reacting with glutathione or redox-active membrane proteins. The interior layer structure of the LbL films during assembly and disassembly is studied by atomic force microscopy (AFM), ellipsometry, dynamic light scattering (DLS), and fluorescence spectroscopy. Insertion of barrier layers in bioreducible LbL films is necessary to stabilize the interior layer structure and slow down the film degradation rate to achieve sequential gene delivery. Localized gene delivery from the LbL films is demonstrated using human embryonic kidney 293 (HEK 293) cells.

Disposable MMP-9 sensor based on the degradation of peptide cross-linked hydrogel films using electrochemical impedance spectroscopy

Matrix metalloproteinase-9 (MMP-9) plays an important role in both physiological and pathological processes. This enzyme is a peripheral biomarker of neuroinflammation in multiple sclerosis (MS), a chronic autoimmune disease of the central nervous system. Presently, expensive magnetic resonance imaging (MRI) studies are used to monitor subclinical disease activity in MS. An alternative to costly MRI scans could be the detection of MMP-9, using a low-cost, disposable sensor system for MMP-9 suitable for home-monitoring of inflammation. This would allow an early prediction of the failure of anti-inflammatory therapies and more timely clinical intervention to limit neuronal damage and prevent disability. Herein we present the development of a disposable sensor for fast and straightforward detection of MMP-9. Biosensors were produced by coating electrodes with oxidized dextran and subsequent cross-linking with peptides containing specific cleavage sites for MMP-9. Exposure of the films to the enzyme resulted in the degradation of the films, which was monitored using impedance measurements. Sensor response was rapid, a significant impedance change was usually observed within 5 min after the addition of MMP-9. Sensors showed a negligible response to matrix metalloproteinase-2 (MMP-2), a protease which may interfere with MMP-9 detection. The peptide sequence with the highest sensitivity and selectivity Leu-Gly-Arg-Met-Gly-Leu-Pro-Gly-Lys was selected to construct calibration curves. MMP-9 was successfully detected in a clinically relevant range from 50 to 400 ng/ml. Two different processes of hydrogel degradation were observed on electrode surfaces with different roughness, and both appeared suitable to monitor MMP-9 activity. The sensor materials are generic and can be easily adopted to respond to other proteases by selecting peptide cross-linkers with suitable cleavage sites.