High-performance bioelectronic tongue using ligand binding domain T1R1 VFT for umami taste detection.

Numerous efforts have been made to measure tastes for various purposes. However, most taste information is still obtained by human sensory evaluation. It is difficult to quantify a degree of taste or establish taste standard. Although artificial taste sensors called electronic tongues utilizing synthetic materials such as polymers, semiconductors, or lipid membranes have been developed, they have limited performance due to their low sensitivity and specificity. Recently, bioelectronic tongues fabricated by integrating human taste receptors and nanomaterial-based sensor platforms have been found to have high performance for measuring tastes with human-like taste perception. However, human umami taste receptor is heterodimeric class C GPCR composed of human taste receptor type 1 member 1 (T1R1) and member 3 (T1R3). Such complicated structure makes it difficult to fabricate bioelectronic tongue. The objective of this study was to develop a protein-based bioelectronic tongue for detecting and discriminating umami taste with human-like performance using umami ligand binding domain called venus flytrap (VFT) domain originating from T1R1 instead of using the whole heterodimeric complex of receptors. Such T1R1 VFT was produced from Escherichia coli (E. coli) with purification and refolding process. It was then immobilized onto graphene-based FET. This bioelectronic tongue for umami taste (BTUT) was able to detect monosodium L-glutamate (MSG) with high sensitivity (ca. 1 nM) and specificity in real-time. The intensity of umami taste was enhanced by inosine monophosphate (IMP) that is very similar to the human taste system. In addition, BTUT allowed efficient reusable property and storage stability. It maintained 90% of normalized signal intensity for five weeks. To develop bioelectronic tongue, this approach using the ligand binding domain of human taste receptor rather than the whole heterodimeric GPCRs has advantages in mass production, reusability, and stability. It also has great potential for various industrial applications such as food, beverage, and pharmaceutical fields.

Size-controllable ultrathin carboxylated polypyrrole nanotube transducer for extremely sensitive 17ß-estradiol FET-type biosensors.

17ß-Estradiol is known as a steroid hormone in the human body but it is also known as a disruptor that can cause disequilibrium and dysfunction of the human immune system. Recently, there has been much interest in developing biosensors to detect low concentrations of 17ß-estradiol. In this work, size-controllable aptamer conjugated ultrathin carboxylated polypyrrole nanotubes (A-UCPPyNTs) were fabricated as transducers in 17ß-estradiol field-effect transistor (FET)-type biosensors. They were manufactured via a self-degradation method under several different conditions to control the diameter of the nanotubes. For targeting 17ß-estradiol, the binding aptamers were immobilized through covalent bonding on its surface. The resulting A-UCPNT FET-type biosensor demonstrated p-type behavior with outstanding electrical conductivity, and exhibited Ohmic contacts between the samples and electrodes. The smaller diameter (40 nm) of ultrathin carboxylated polypyrrole nanotubes (UCPPyNTs) contributed to the biosensor's enhanced performance by generating a larger surface area, thereby increasing the number of conjugated binding aptamers. In conclusion, the A-UCPPyNT FET-type biosensor showed extremely high sensitivity (∼1 fM) toward 17ß-estradiol, approximately 103 times more sensitive than the results found in other reports. Moreover, the A-UCPPyNT FET-type biosensor showed unique selectivity to the 17ß-estradiol molecule, in addition to outstanding reusability and long-term storage stability (4 weeks of duration achieved in this work). These performances concerned with reusability and stability were achieved by the formation of covalent bonding in the anchorage to the substrate electrode. Thus this study can be effectively applied in biological and environmental fields.