Conducting Polymer Coating Turns Ordinary Electrode Into Ultra-Sensitive Detector of Bladder Drug

Overactive bladder is one of the most common yet under-discussed chronic conditions in modern medicine, defined by the International Continence Society through its hallmark symptoms of urinary urgency and increased frequency of urination. In the United States alone, more than 16 percent of adults are affected, and the burden extends into pediatric care, where antimuscarinic drugs such as oxybutynin hydrochloride are prescribed for cases including spina bifida. For a drug that has been in clinical use for five decades, the analytical toolkit available to measure it has lagged surprisingly behind. Now, a team of researchers in India has reported an electrochemical sensor so sensitive that it can detect oxybutynin hydrochloride at concentrations as low as 9.16 nanomolar, using an inexpensive conducting polymer coating on a standard glassy carbon electrode.

The study, published in the journal Discover Electrochemistry, was led by Sandeep Kurundawade and Sharanappa T. Nandibewoor of KLE Technological University in Hubballi, together with colleagues at Atria Institute of Technology in Bengaluru and J.S.S. Banashankari Arts, Commerce and S.K. Gubbi Science College in Dharwad. Their choice of modifier was polyaniline, one of the oldest and best understood conducting polymers. Polyaniline is prized in materials science for its unique p-type doping chemistry, its reversible redox transitions between the leucoemeraldine, emeraldine and pernigraniline states, and its protonic conductivity, all of which allow it to alter the electronic behavior of an electrode surface. Compared with its polymeric cousins polypyrrole and polythiophene, polyaniline also offers superior environmental resilience, an essential property for a sensor intended for repeated laboratory use.

Synthesis of the polymer followed a classical route: oxidative polymerization of aniline in 1.5 molar hydrochloric acid, initiated by the gradual, drop-wise addition of ammonium persulphate while the reaction mixture was stirred. The slow addition is not decorative; it prevents over-oxidation and promotes uniform chain growth. The reaction mixture’s shift to the characteristic dark green color of polyaniline’s emeraldine salt signaled success. The researchers then characterized the product with scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Electron microscopy revealed a cohesive network of uniformly packed spherical agglomerates, while the diffraction pattern showed a broad peak near 2θ equal to 25 degrees, a signature of the polymer’s π-π stacked aromatic framework and its mildly crystalline, emeraldine-phase structure.

The heart of the sensor is a glassy carbon electrode, a workhorse of electroanalytical chemistry with a geometric area of just 0.09 square centimeters. A 1 milligram sample of polyaniline was dispersed in dimethylformamide by sonication and drop-cast onto the polished electrode, with the deposited volume optimized at 4 microliters after testing across a 2 to 8 microliter range. To measure how much the coating enlarged the electrochemically active surface, the team employed a ferricyanide redox probe and the Randles-Sevcik equation. The bare electrode’s active area was 0.04 square centimeters; with polyaniline it grew to 0.156 square centimeters, a 4.4-fold increase that translates into a far denser network of electroactive sites and correspondingly faster charge transfer.

Impedance measurements reinforced that picture. Nyquist plots, fitted to a Randles equivalent circuit, yielded charge transfer resistance values of 17.03 ohms for the bare electrode and 11.57 ohms for the modified one, while the calculated heterogeneous charge transfer rate constants rose from 1.56 × 10⁻⁵ to 2.3 × 10⁻⁵ centimeters per second and exchange currents climbed from 1.508 × 10⁻³ to 2.219 × 10⁻³ amperes. In plain terms, the polymer film does not merely add surface area; it actively lubricates the movement of electrons between the drug molecules in solution and the electrode beneath. An immersion-time study further showed that the analytical signal peaked after 40 seconds of accumulation, beyond which the response declined, likely because the available surface had saturated or an inhibitory molecular layer had formed.

With the hardware characterized, the team turned to the electrochemistry of oxybutynin itself. Cyclic voltammetry in phosphate buffer at pH 7.4, scanned between 0.5 and 1.5 volts, produced a single anodic peak with no counterpart on the reverse scan, marking the oxidation as irreversible. On the modified electrode the peak current reached 76.7 microamperes against 42.6 microamperes on bare glassy carbon, and the peak potential shifted slightly downward from 1.191 to 1.185 volts, evidence that polyaniline lowers the overpotential and eases the oxidation. Varying the pH from 3.0 to 9.2 revealed a maximum response at 7.4, close to physiological pH, and a peak potential that tracked pH with a slope of 64 millivolts per pH unit, near the Nernstian ideal of 59, indicating equal numbers of electrons and protons in the reaction.

Scan rate studies completed the mechanistic portrait. The peak current scaled linearly with the square root of the scan rate, and a log-log analysis produced a slope of 0.3285, close to the theoretical value of 0.5 for diffusion control. Applying the Laviron equation to the relationship between peak potential and scan rate gave a transfer-coefficient-electron product of 1.14, which resolved to approximately two electrons when the standard transfer coefficient of 0.5 was assumed. Combined with the pH result, the oxidation of oxybutynin at the modified electrode is therefore a diffusion-controlled, irreversible process involving two electrons and two protons, proceeding through successive electron-transfer and deprotonation steps toward an oxidized imine-type intermediate and ultimately an amine-based product.

The analytical performance is where the sensor earns its headline. Using square-wave voltammetry, a technique prized for its ability to reject background currents, the team recorded a linear response across 0.04 to 10 micromolar oxybutynin, with a detection limit of 9.16 nanomolar and a limit of quantification of 30.5 nanomolar, calculated by the standard equations based on the regression intercept’s standard deviation. That sensitivity compares favorably with previously reported oxybutynin sensors, which the authors note have tended to be either expensive, laborious to construct, or both. Selectivity testing with 100-fold excesses of citric acid, gum acacia, D-glucose, dopamine, L-ascorbic acid, sucrose, and common inorganic salts produced peak potential shifts all below the 2 percent tolerance limit, confirming the sensor’s robustness in messy real-world matrices.

The practical demonstrations may prove the most consequential part of the work. Pulverized commercial 5 milligram tablets, dissolved and diluted into the linear range, yielded recoveries in excellent agreement with the label claim, opening the door to routine pharmaceutical quality control. Human urine diluted 100-fold and spiked with known drug concentrations, along with tap water, Krishna River water from Belagavi in Karnataka, and RO-purified water, were all analyzed with acceptable recoveries, extending the sensor’s reach into pharmacokinetic monitoring and environmental surveillance of pharmaceutical contamination. Stability testing showed consistent within-day signals and retention of a high percentage of the initial response after 15 days of storage in a sealed container. Taken together, the results suggest that a coating of a cheap, easily synthesized conducting polymer can transform a routine glassy carbon electrode into a precision instrument, one well suited to clinical laboratories, quality control departments, and environmental monitoring programs that have historically been priced out of high-sensitivity drug analysis.

Subject of Research: Ultrasensitive electrochemical detection of the drug oxybutynin hydrochloride using a polyaniline-modified glassy carbon electrode sensor

Article Title: Ultrasensitive electrochemical detection of oxybutynin hydrochloride using polyaniline modified sensor

Article References: Kurundawade, S., Megalamani, M. B., Naik, K., Yaraguppi, D. A., & Nandibewoor, S. T. (2026). Ultrasensitive electrochemical detection of oxybutynin hydrochloride using polyaniline modified sensor. Discover Electrochemistry, 3(1), Article 73. https://doi.org/10.1007/s44373-026-00161-y

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00161-y

Keywords: oxybutynin hydrochloride, polyaniline, electrochemical sensor, glassy carbon electrode, square-wave voltammetry, cyclic voltammetry, overactive bladder, pharmaceutical analysis, detection limit, conducting polymer, electrocatalysis, pharmacokinetics