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The discovery that synthetic short chain nucleic acids are capable of selective binding to biological targets has made them to be widely used as molecular recognition elements. These nucleic acids, called aptamers, are comprised of two types, DNA and RNA aptamers, where the DNA aptamer is preferred over the latter due to its stability, making it widely used in a number of applications. However, the success of the DNA selection process through Systematic Evolution of Ligands by Exponential Enrichment (SELEX) experiments is very much dependent on its most critical step, which is the conversion of the dsDNA to ssDNA. There is a plethora of methods available in generating ssDNA from the corresponding dsDNA. These include asymmetric PCR, biotin-streptavidin separation, lambda exonuclease digestion and size separation on denaturing-urea PAGE. Herein, different methods of ssDNA generation following the PCR amplification step in SELEX are reviewed.

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Epoxidized soybean oil (ESO) was thermally cured using methylhexahydrophthalic anhydride (MHHPA) curing agent in the presence of 2-ethyl-4-methylimidazole (EMI) catalyst. The curing characteristics of ESO/MHHPA/ EMI systems were characterized using Fourier transform infrared spectroscopy (FTIR), a dynamic mechanical analyzer (DMA) and a differential scanning calorimeter (DSC). FTIR spectra showed that the polyesterification rate in ESO/MHHPA/EMI systems increased with increasing of the catalyst concentration. DSC thermograms indicated that EMI-catalyzed ESO/MHHPA systems experienced enthalpy relaxation at low EMI concentration whereas the extent decreased with increasing of the EMI concentration. There is a direct relationship between the degree of conversion and crosslink density of the thermal cured ESO/MHHPA/EMI systems with EMI concentration. The curing characteristics of thermal curable ESO thermosetting resins were found to have influence on the thermal properties of the ESO systems. It was determined that the glass transition temperature (T g ) and storage modulus (E 0 ) of cured ESO increased with increasing the EMI concentration whereas the damping properties of the ESO/MHHPA/EMI systems exhibited the reverse trend. It was found that the thermally curable ESO thermosetting resins experienced a two-stage thermal decomposition process.

The generation of DNA aptamer by Systematic Evolution of Ligands by Exponential Enrichment requires a good method of ssDNA generation. There are various methods developed to generate ssDNA such as streptavidin-biotin based separation techniques, asymmetric PCR and strand separation of the PCR product containing primer with a terminator and an extension of 20 nucleotides on denaturing urea-polyacrylamide gel. In the present investigation, we have shown the possible improvements for the regular lambda nuclease digestion under optimized conditions. Optimization of the PCR cycles, time course studies on lambda nuclease digestion and purification of the ssDNA from the lambda exonuclease digestion mixture was found to be able to recover ssDNA amounting up to 39.19 ± 2.48 % of the starting amount of dsDNA. These strategies can be applied to the techniques involving essential usage of ssDNA.

Epoxidized soybean oil (ESO) was successfully thermal-cured by using methylhexahydrophthalic anhydride (MHHPA) curing agent, in the presence of tetraethylammonium bromide (TEAB) catalyst of varied concentration (0.3–0.8 phr). The polyesterification process of ESO thermoset was proven and supported by Fourier transforms infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy analysis (GC-MS). A possible chemical reaction of the MHHPA, TEAB and ESO was proposed based on the experimental work. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed that there is a positive relationship between the degree of conversion and crosslink density of ESO thermoset with TEAB concentration. The kinetics of water absorption of the ESO thermoset were found to conform to Fickian law behavior

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