In vitro selection of DNA aptamers for the development of fluorescent aptasensor for sarcosine detection

In order to develop a simple, convenient and economic method to detect and quantify the level of sarcosine in human urine samples, we have selected DNA aptamers for sarcosine through a modified affinity chromatography SELEX (Systematic Evolution of Ligands by Exponential Enrichment), which is based on the aptamer sequences bound by the target molecules would be released from the DNA hybridizations coupled on streptavidin-agarose beads. 4 aptamer candidates were obtained after 12 rounds of selection, and their affinities were preliminarily checked by SYBR green I staining. The best of them is Sar11, which with the dissociation constant (K-d) of 134.8 nM was further modified and used to design a fluorescence sensor to quantify sarcosine. The detection limit of sarcosine by this sensor is 55 nM, while its quantitative range is 100 to 2000 nM. Also, the aptamer Sar11 shows good selectivity for sarcosine to its analogues. Moreover, the fluorescent aptasensor obtains a satisfying result for the detection of sarcosine in human urine samples.