Ultrasensitive Stress Biomarker Detection Using Polypyrrole Nanotube Coupled to a Field-Effect Transistor.

Stress biomarkers such as hormones and neurotransmitters in bodily fluids can indicate an individual's physical and mental state, as well as influence their quality of life and health. Thus, sensitive and rapid detection of stress biomarkers (e.g., cortisol) is important for management of various diseases with harmful symptoms, including post-traumatic stress disorder and depression. Here, we describe rapid and sensitive cortisol detection based on a conducting polymer (CP) nanotube (NT) field-effect transistor (FET) platform. The synthesized polypyrrole (PPy) NT was functionalized with the cortisol antibody immunoglobulin G (IgG) for the sensitive and specific detection of cortisol hormone. The anti-cortisol IgG was covalently attached to a basal plane of PPy NT through an amide bond between the carboxyl group of PPy NT and the amino group of anti-cortisol IgG. The resulting field-effect transistor-type biosensor was utilized to evaluate various cortisol concentrations. Cortisol was sensitively measured to a detection limit of 2.7 × 10-10 M (100 pg/mL), with a dynamic range of 2.7 × 10-10 to 10-7 M; it exhibited rapid responses (<5 s). We believe that our approach can serve as an alternative to time-consuming and labor-intensive health questionnaires; it can also be used for diagnosis of underlying stress-related disorders.

High-Performance Conducting Polymer Nanotube-based Liquid-Ion Gated Field-Effect Transistor Aptasensor for Dopamine Exocytosis.

In this study, ultrasensitive and precise detection of a representative brain hormone, dopamine (DA), was demonstrated using functional conducting polymer nanotubes modified with aptamers. A high-performance aptasensor was composed of interdigitated microelectrodes (IMEs), carboxylated polypyrrole nanotubes (CPNTs) and DA-specific aptamers. The biosensors were constructed by sequential conjugation of CPNTs and aptamer molecules on the IMEs, and the substrate was integrated into a liquid-ion gating system surrounded by pH 7.4 buffer as an electrolyte. To confirm DA exocytosis based on aptasensors, DA sensitivity and selectivity were monitored using liquid-ion gated field-effect transistors (FETs). The minimum detection level (MDL; 100 pM) of the aptasensors was determined, and their MDL was optimized by controlling the diameter of the CPNTs owing to their different capacities for aptamer introduction. The MDL of CPNT aptasensors is sufficient for discriminating between healthy and unhealthy individuals because the total DA concentration in the blood of normal person is generally determined to be ca. 0.5 to 6.2 ng/mL (3.9 to 40.5 nM) by high-performance liquid chromatography (HPLC) (this information was obtained from a guidebook "Evidence-Based Medicine 2018 SCL " which was published by Seoul Clinical Laboratory). The CPNTs with the smaller diameters (CPNT2: ca. 120 nm) showed 100 times higher sensitivity and selectivity than the wider CPNTs (CPNT1: ca. 200 nm). Moreover, the aptasensors based on CPNTs had excellent DA discrimination in the presence of various neurotransmitters. Based on the excellent sensing properties of these aptasensors, the DA levels of exogeneous DA samples that were prepared from PC12 cells by a DA release assay were successfully measured by DA kits, and the aptasensor sensing properties were compared to those of standard DA reagents. Finally, the real-time response values to the various exogeneous DA release levels were similar to those of a standard DA aptasensor. Therefore, CPNT-based aptasensors provide efficient and rapid DA screening for neuron-mediated genetic diseases such as Parkinson's disease.

Fluorescent polydopamine nanoparticles as a probe for zebrafish sensory hair cells targeted in vivo imaging.

Fluorescent polydopamine nanoparticles (FPNPs) are prepared via the ethylenediamine (EDA)-induced degradation of as-prepared non-fluorescent polydopamine (PDA) and used for targeted bioimaging. The reductive treatment of PDA in the presence of EDA yields fluorescent precipitates, inspiring us to seek various biological approaches to preparing FPNPs with excellent optical and biocompatible properties. Moreover, we firstly found that FPNPs selectively label neuromast hair cells in the lateral line of zebrafish, their applications as a reliable fluorescent indicator to investigate the neuromast hair cells, to in turn determine the viability of hair cells, was demonstrated. FPNPs also provided a minimal toxicity enable to assay the number of functional hair cells per neuromast in live animals as development proceeds. Upon combined incubation with TO-PRO-3, a well-established hair cell marker, all hair cells that were rapidly labeled with FPNPs were observed to be also completely labeled with the TO-PRO-3, labeling hair cells in neuromasts positioned in the supraorbital, otic and occipital lateral line as well as in posterior lateral line of living zebrafish larvae. Their potential efficacy for biological applications was demonstrated by their excellent optical and biocompatible properties, offering new opportunities in cancer research, real-time monitoring of stem cell transplantation and other cell-based therapies.

Carboxylic Acid-Functionalized Conducting-Polymer Nanotubes as Highly Sensitive Nerve-Agent Chemiresistors.

Organophosphates are powerful inhibitors of acetylcholinesterase, which is critical to nerve function. Despite continuous research for detecting the highly toxic organophosphates, a new and improved methodology is still needed. Herein we demonstrate simple-to-fabricate chemiresistive gas sensors using conducting-polymer polypyrrole (PPy) nanotube transducers, which are chemically specific and capable of recognizing sub-ppb concentrations (ca. 0.5 ppb) of dimethyl methylphosphonate (DMMP), a simulant of nerve agent sarin. Interestingly, the introduction of carboxylic groups on the surface of PPy nanotube transistors resulted in enhanced sensitivity to DMMP via intermolecular hydrogen bonding. Furthermore, it was found that the sensitivity of the nanotube transducer depended on the degree of the carboxylic group introduced. Finally, a sensor array composed of 5 different transducers including the carboxylated nanotubes exhibited excellent selectivity to DMMP in 16 vapor species.