Current colorimetric presumptive identification of illicit drugs for determining illegal possession of controlled substances by law enforcement relies solely on the subjective interpretation of color change using drug- or class-specific reactions. Here, we describe the use of inexpensive polyester-toner, rotation-driven microfluidic devices with a smartphone as a potential alternative for current presumptive colorimetric field-testing of illicit drugs, allowing for an objective and user-friendly image analysis technique for detection. The centrifugal microfluidic platform accommodates simultaneous presumptive testing of material from a single input to multiple reaction chambers, enabling rapid screening. Hue and saturation image analysis parameters are used to define threshold values for the detection of cocaine and methamphetamine as proof-of-principle with 0.25 and 0.75 mg/mL limits of detection, respectively, with nonvolatile reagents stored on-board and smartphone for detection. Reported LODs are lower than those concentrations used in the field. Additionally, the developed objective detection method addresses the testing of drugs with various common cutting agents, including those known to produce false negative and positive results. We demonstrate the effectiveness of the method by successfully identifying the composition of 30 unknown samples.
Fzo1, a large GTPase of the Dynamin-Related Proteins superfamily, is a key component in mitochondrial outer membrane fusion and is required for maintaining mitochondrial dynamics and morphology. The protein is anchored to the outer membrane by two transmembrane segments and its N-terminal GTPase domain and C-terminal are exposed to the cytosol. Recent data indicate that the GTPase domain of Fzo1 would induce a conformational change concomitant with mitochondrial tethering, thus promoting membrane fusion [1]. We investigate the structure and dynamics of Fzo1 through molecular modeling and all-atom simulation in a model mixed lipid bilayer, closely linked to experiments. Our structural model integrates information from several template structures, experimental knowledge, as well as ab initio models of the transmembrane segments that are unique to Fzo1. The model is validated experimentally through charge swap mutations across predicted salt bridges and a series of N-terminal truncation mutants indicates that this region is dispensable for function. Our approach unravels hinges domains involved in the conformational change and identified critical residues required for protein stability. Moreover several point mutation found to disrupt the architecture of the protein are located in the coiled-coil domain which has been shown fundamental for the protein [2]. Finally, we dissected key residues in protein-GDP interaction providing fundamental insights about molecular mechanisms by which mitofusins catalyze membrane fusion.
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