Development of an electrochemical signal-on aptasensor for selective detection of tryptophan

Tryptophan (Trp) is a necessary amino acid which is required for normal growth, nitrogen equilibrium and brain functions in humans [1]. It is also used as a precursor for melatonin, serotonin and niacin [2]. Regrettably, when it was incorrectly metabolized, it begets a toxic product in the brain that makes schizophrenia, hallucinations and delusions [3]. On the other hand, because the concentration of Trp in biological samples is low, therefore, there is an urgent need for rapid, easy, sensitive, selective and less expensive techniques for quantification of Trp. In recent years, in order to solve many of these challenges, a new class of ligands, called aptamers, is known to detect specific molecular targets. Aptamers possess several advantages that make it an ideal biosensing element such as improved temperature stability, shelf life, easy synthesis, flexible to modification, easy storage, low toxicity, more stable to biodegradation and high binding tendency and selectivity [4]. Among various aptamer-based biosensors, electrochemical aptasensors have received an increasing amount of attention for detection of analytes due to their high sensitivity, simplicity, portability, low expense and rapid response for molecular detection [5]. In the development of chemical sensors, among the many types of nanoparticles, silica is highly regarded. Silica nanoparticle (SN) can be grafted with a various types of functional groups, in order to immobilize different biomolecules such as enzymes, proteins, antibodies and DNA [6]. In this study, a simple and label-free signal-on electrochemical aptasensor is designed for sensitive and selective electrochemical detection of Trp based on the covalent attachment of 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 34 aptamer, as recognition molecule, on AuNPs/SiO2-pr-NH2/SPE and using hemin and [Fe (CN6)]3-/4- electrochemical probes, for “signal on” strategy. The linear range of proposed aptasensor based on “signal on” mechanisms using “DPV” and “EIS” methods were 0.06–250 nM with corresponding LODs 0.026 and 0.01nM, respectively. The introduced strategy has several attractive advantages simultaneously such as: simplicity, fast response, no requirement for a specific label, inexpensive, efficient sensitivity, high selectivity, a useful method in medical diagnosis and it is a signal-on sensor with acceptable stability.