2.3. Preparation of Aptamer and Modified AuNPs
A Paper-Based Colorimetric Aptasensor for the Detection of Gentamicin
Biosensors (Basel), Jan 21, 2021; DOI: 10.3390/bios11020029

The aptamers were received in the form of a dry pellet. During the resuspension procedure, the aptamer vial was first centrifuged at 10,000 rpm for 30 s. To obtain a total stock concentration of 100 µM, 8 mL of Tris-EDTA buffer (10 mM Tris, 0.1 mM EDTA, pH 7.5) was prepared. This solution was briefly heated in a double boiler set up to uncoil the DNA oligos at 70 °C. It was allowed to cool back to room temperature for 20 min and later stored at −20 °C for further experiments. The stock solution was diluted to 1 µM working solution maintained at pH7.4 for all consecutive experimentation. A 96-well plate setup for full spectral analyses were used to as proof of concept. All optimizations were first conducted in a 96-well plate format and further applied on a paper substrate. Fresh dilutions of gentamicin were prepared in 1X TE pH 7.4, ranging from 3 µM to 1 nM from 10 µM stock solutions. The absorbance ratio of A640/A520 was calculated to plot the standard curve for the sensor and derive its sensitivity.