Biodiesel has received tremendous attention as a sustainable energy source. This review presents an overview of various catalysts utilized in biodiesel production and compares their potential for producing biodiesel. Presented here are the excellent features of the various catalysts while highlighting their drawbacks. For instance, production of biodiesel with homogeneous base catalysts is easy but it can only be used with refined oils having low levels of free fatty acid (FFAs). When homogeneous acid is used in esterification, it causes reactor corrosion. Water and FFAs do not affect heterogeneous acid catalysts. Thus, transesterification of triglycerides into biodiesel and converting FFAs into biodiesel through esterification can be catalyzed more efficiently using a heterogeneous acid catalyst. Biocatalysts are also being used to produce biodiesel from oils with high FFAs. However, heterogeneous acid catalysts and biocatalysts are not suitable for industrial application due to serious mass transfer limitations. Biodiesel yield and conversion were compared over various catalysts in this paper. Also presented are the effects of different reaction parameters on biodiesel yield over different catalysts. The correct interplay of factors like reaction temperature, time, alcohol-to-oil molar ratio, and catalyst loading produces optimal process conditions that give the highest biodiesel yield.

We report a universal smart probe (SP) that is capable of detecting several homologous let-7 microRNAs (miRNAs). While the SP is complementary to let-7a, and therefore, strongly binds to this target, due to sequence homology, the SP also has equal propensity to non-specifically hybridize with let-7b and let-7c, which are homologous to let-7a. The fluorescence signal of the SP was switched off in the absence of any homologous member target, but the signal was switched on when any of the three homologous members was present. With the assistance of nucleic acid blockers (NABs), this SP system can discriminate between homologous miRNAs. We show that the SP can discriminate between let-7a and the other two sequences by using linear NABs (LNABs) to block non-specific interactions between the SP and these sequences. We also found that LNABs used do not cross-react with the let-7a target due to the low LNABs:SP molar ratio of 6:1 used. Overall, this SP represents a universal probe for the recognition of a homologous miRNA family. The assay is sensitive, providing a detection limit of 6 fmol. The approach is simple, fast, usable at room temperature, and represents a general platform for the in vitro detection of homologous microRNAs by a single fluorescent hairpin probe.