27th August 2019

Malaria is a serious life threatening disease, affecting a large portion of the population in developing countries. Over the last decade, there has been a continuous effort to develop efficient, stable, sensitive and low cost detection system for malaria. Currently, lateral flow based immuno-chromatographic tests are widely used for detection of malaria. However, these antibody-based tests are usually non-quantitative in nature and their stability is impaired in hot and humid environment. Nucleic acid aptamers have been shown as an efficient and viable alternative to overcome these limitations because of their increased chemical stability and high affinity towards the target. Furthermore, the unique binding properties of aptamers have shown great potential for biosensors using optical, electrochemical, and mass-sensitive approaches.

Taking advantage of aptamers and enhanced sensitivity of electrochemical biosensor such as field effect transistor (FET), Singh et al., 2018 developed an easy point-of-care platform for sensitive detection of malaria biomarker Plasmodium falciparum glutamate dehydrogenase (PfGDH) in serum samples. A 90 nucleotide long ssDNA aptamer was selected against PfGHD after performing 17 rounds of SELEX cycles, including rounds of negative selection against PVDF membrane and human glutamate dehydrogenase (HGDH). Using this aptamer, the authors developed aptamer based field transistor (aptaFET) with inter-digitated gold microelectrodes (IDμE) to capture the target protein (Figure 1).

Figure 1. Schematic representation of aptaFET for detection of PfGDH in blood serum.

The aptamer was immobilised via gold-thiol chemistry on IDµE connected to the gate of a transistor. The intrinsic surface net charge of the captured protein led to change in gate potential of the aptaFET device, which correlated to the concentration of PfGDH protein in diluted serum (10 fold) (Fig 2A & 2B). The device was able to offer results in seconds (5s) and was able to detect PfGDH at a picomolar level (48.6 pM), with broad detection range of 100 fM-10 nM in diluted serum samples. The high selectivity of biosensor for PfGDH was verified by testing relevant analogous human and parasite proteins on the device (Figure 2C & 2D).

Figure 2. AptaFET response against different concentrations of PfGDH protein spiked in serum (A) with corresponding calibration plot (B). AptaFET response against different potential interfering proteins (C) showing higher selectivity for the target PfGDH protein (D) as compared to other closely related analogous proteins.

Overall the results validated the application potential of the developed aptaFET for diagnosis of both symptomatic and asymptomatic malaria. Moreover, the smaller size of the aptamer in the FET helped to overcome a common problem (Debye restriction) caused when larger antibodies are used. At Aptamer Group, we are involved in continuous development of similar biosensors for protein biomarkers and even small molecule detection using our high affinity aptamers. If you would like more information on such platforms, please contact us using the form below.

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Reference:

Singh, N., Thungon, P., Estrela, P. and Goswami, P. (2018). Development of an aptamer-based field effect transistor biosensor for quantitative detection of Plasmodium falciparum glutamate dehydrogenase in serum samples. Biosensors and Bioelectronics, 123, pp.30-35.