Iodine is an essential micronutrient in modulating critical functions of the body, such as producing thyroid hormones. A deficiency of iodine can cause severe thyroid-related disorders , while high doses of iodine can trigger overproduction of thyroid hormones, increasing the risk of developing thyroid dysfunction [1,2]. Therefore, it is critical to assess the iodine concentration in body fluids to monitor and diagnose early signs of diseases. Here we report on a simple, rapid, and highly-sensitive electrochemical detection of urinary iodine (UI) by exploiting the exceptional electrocatalytic capabilities of stress-activated pyrolytic carbon nanofibers (SAPCs). SAPCs are synthesized by stress-induced molecular alignment and subsequent low-temperature pyrolysis of organic carbon precursors. The resulting carbon possesses highly-graphitic structures that are characteristically rich in nitrogen heteroatoms and edge planes [3,4]. The tunable surface of SAPCs can also enhance the sensitivity and specificity of iodide ions in human urine. Furthermore, the high macroporosity of SAPCs increases surface area, creating a large liquid-carbon junction in aqueous solutions, providing efficient ion transport and adsorption capacity. The sensitivity and limit of detection (LoD) of SAPCs were evaluated by obtaining the linearity of molar concentration of iodide ions (I-) vs. current. The sensor specificity of SAPCs electrode for iodide ions was also investigated by adding a series of competitive anions such as F-, Cl-, PO43-, HPO42-, and H2PO4- into the solution and evaluating the effect of interference substances electrochemically. Additionally, the reproducibility of SAPCs for iodide ion detection was assessed by measuring the inter- and intra- coefficients of variability (CV%).
The need for sensitive, portable diagnostic tests at the point of care persists. We report on a simple method to obtain improved detection of biomolecules by a two-fold mechanism. Silica (SiO2) is coated on pre-stressed thermoplastic shrink-wrap film. When the film retracts, the resulting micro- and nanostructures yield far-field fluorescence signal enhancements over their planar or wrinkled counterparts. Because the film shrinks by 95% in surface area, there is also a 20x concentration effect. The SiO2 structured substrate is therefore used for improved detection of labeled proteins and DNA hybridization via both fluorescent and bright field. Through optical characterization studies, we attribute the fluorescence signal enhancements of ~100x to increased surface density and light scattering from the rough SiO2 structures. Combining with our open channel self-wicking microfluidics, we can achieve extremely low cost yet sensitive point of care diagnostics.