Netzahualcóyotl Arroyo-Currás

Real-time, continuous monitoring of large peptide and protein biomarkers has transformative potential for personalized medicine but is hindered by the rapid degradation of affinity-based sensors in complex biofluids. While physical barriers such as size-exclusion membranes can mitigate biofouling, they also exclude the high-molecular-weight proteins to be measured, creating a fundamental paradox for sensor design. Here, we present a solution to this stability-fouling trade-off: a “mixed charge” monolayer interface that confers multi-week fouling resistance without relying on physical filtration. By incorporating compact amine- and carboxyl-terminations onto 8-carbon alkyl thiolates, we engineered a surface that mimics zwitterionic hydration while preserving the dense molecular packing and intermolecular forces required for long-term monolayer stability. This architecture extends the operational lifetime of electrochemical aptamer sensors to 14 days in whole serum. Sensors targeting the small molecule cortisol retained ∼80% of their initial analyte response signal gain, while those targeting the protein platelet-derived growth factor bb (PDGF-bb) preserved nearly 100% of their analyte response signaling capacity over the two-week period. These findings demonstrate a generalized, membrane-free platform capable of robust, multi-week molecular monitoring of larger peptides and proteins.

Aptamer-based molecular monitors enable continuous, real-time tracking of analytes in complex environments, including in vivo, but their practical deployment is limited by short operational lifetimes of only hours. This instability arises in part from the electrochemical interrogation of the aptamer-bound redox reporter methylene blue, whose standard potential overlaps with oxygen reduction on gold electrodes, leading to peroxide generation and, concomitantly, accelerated sensor degradation. We previously demonstrated that peroxide accumulates to tens-to-hundreds of micromolar on the sensor surface under typical operating conditions. Here, we address this limitation by rationally designing redox reporters with more positive standard potentials, beyond the range of oxygen electroreduction. Using electron-withdrawing substituents and extended conjugation strategies, we developed a new reporter, Netz Lab Blue, exhibiting a standard potential 160 mV more positive than methylene blue. Aptamer-based monitors incorporating Netz Lab Blue withstand ≥10,000 interrogation cycles in buffered saline without measurable signal loss, whereas methylene blue-based sensors lose >20% signal under identical conditions. In oxygen-saturated solutions, Netz Lab Blue-based sensors retain full stability over the same duty cycle while methylene blue-based devices fail completely. Additionally, Netz Lab Blue delivers 40% higher signal gain for the same aptamer sequence and under identical packing density relative to methylene blue. These improvements translate directly to biological environments, where Netz Lab Blue‑based sensors exhibit stable performance in rat blood and support continuous, real‑time in vivo drug monitoring in the brain of rodents using two distinct aptamer sensors. By eliminating peroxide generation during electrochemical interrogation, this new redox reporter markedly extends sensor lifetime and performance, potentially enabling continuous molecular monitoring over days to weeks in biomedical applications that seek to interrogate human physiology.

To celebrate the 250th Electrochemical Society Meeting in Calgary, we asked members from around the globe to give us their thoughts on what ECS meetings mean to them. The contributors to this Interface issue come from different countries and divisions and range in age and experience, but as we read through the essays, some common themes emerged: memories of presentations using transparencies and overhead projectors(!), awestruck students meeting and talking to Nobel Prize winners and renowned scientists between sessions, and friendships and collaborations forged and maintained over the years. While science and technology are at the forefront of any ECS Meeting, it’s those personal connections that people cherish the most.

Characterizing drug distribution to target organs is of central importance to drug discovery, especially for compounds intended to reach the central nervous system (CNS). However, the current benchmark standard measurements, based on tissue homogenate, provide limited spatial and temporal resolution. Here, we use real-time electrochemical aptamer-based (E-AB) monitoring to determine drug concentrations across specific brain regions, blood, and liver of rats after intravenous dosing. Using vancomycin and tobramycin as models, we reveal significant regional differences in brain pharmacokinetics. Vancomycin shows distinct kinetics across cortex, hippocampus, and thalamus, crossing the blood−brain barrier (BBB) but showing limited transport across the blood−cerebrospinal fluid barrier (BCSFB). Tobramycin, despite its smaller size, fails to cross either barrier. Vancomycin’s liver distribution is delayed and limited, resembling its brain kinetics more than blood. These findings challenge assumptions of uniform CNS drug distribution and fast liver uptake, highlighting the need for spatially and temporally resolved pharmacokinetic assessments. Our approach enables high-resolution, in vivo profiling of drug absorption, distribution, and clearance, offering a powerful tool to inform dosing strategies and improve translational outcomes.

A rationally designed DNA hairpin sensor converts intercalator binding into an electrochemical signal through target-induced hairpin stabilization. The platform selectively identifies DNA intercalators over minor groove binders.

Traditional enzyme-linked immunosorbent assays (ELISAs) rely on horseradish peroxidase (HRP)-conjugated antibodies to generate a colorimetric response proportional to target antibody concentration. However, spectrophotometric quantification requires expensive benchtop equipment, limiting its usability for frequent, population-scale immunity screening. To overcome this barrier, we previously developed LC15, an antibody–invertase fusion protein that catalyzes sucrose-to-glucose conversion in proportion to antibody levels. This fusion protein enabled antibody quantification using handheld glucometers – affordable, widely available devices already integrated with telehealth infrastructure. Unlike commercial ELISAs, which report relative antibody titers, LC15 facilitates absolute antibody quantification (μg mL⁻¹), enhancing applications such as epidemiological monitoring and convalescent plasma dosing. To increase the number of clinical samples processed in a single run of the assay, in this study we transitioned from poly(methyl methacrylate) strips to microwell plates, optimizing pH conditions and reagent concentrations. This adaptation yielded similar sensitivity to the original strip-based assay, but with a 5-fold reduction in reagent consumption and in plasma, as opposed to serum used for the previous study. Using the SARS-CoV-2 receptor binding domain (RBD) as the antigen, we applied LC15 in a 96-well plate format to screen 72 clinical samples in triplicate for anti-RBD antibodies. A blinded comparison with commercial ELISAs demonstrated strong linear correlation (R² = 0.85) over four orders of magnitude in concentration. By combining accuracy with accessibility, this approach has the potential to facilitate population-level immunity assessments, supporting rapid public health responses in future outbreaks.

Electrochemical aptamer-based (E-AB) sensors can continuously monitor drug concentrations with high temporal resolution. While previous studies have successfully demonstrated in vivo molecular monitoring using E-AB sensors, they typically rely on custom-built probes fabricated through manual, labor-intensive processes. Constructing such probes requires substantial time, technical expertise, and precision, creating a high barrier to entry for researchers interested in the field of in vivo measurements. To address this limitation, we present an alternative fabrication approach that combines established device construction methods with rapid prototyping via additive manufacturing (i.e., stereolithography). This platform enables continuous molecular monitoring in the subcutaneous interstitial fluid (ISF) of rodent models. We selected ISF as a target fluid due to its growing recognition as a promising frontier for continuous molecular monitoring and its central role in current biosensor research. Our goal is to eliminate the most prohibitive steps in traditional fabrication, thereby reducing the skill threshold required for building functional E-AB probes. By improving the construction process, our methods should make the technology more easily adoptable by a broader range of research laboratories. Ultimately, we aim to broaden the use of E-AB sensors and accelerate development in the field of real-time, in vivo molecular monitoring.

Nucleic acid-based sensors (NBEs) are used for biomolecular detection and can enable continuous, real-time molecular monitoring in vivo. NBEs are typically constructed via thiol self-assembled monolayers (SAMs) on gold electrodes, consisting of redox-reporter-modified oligonucleotides diluted within an alkylthiol monolayer. However, the limited stability of thiol SAMs when chronically exposed to biological fluids restricts the long-term in vivo lifespan of NBEs. In contrast, N-heterocyclic carbenes (NHCs) are monolayer-forming ligands that offer improved surface stability versus thiols for biological applications, but to date, the synthetic routes to attach biomolecules to NHC surfaces rely solely on azides tethered to the NHC. As an alternative, employing strain-promoted azide-alkyne cycloadditions (SPAAC) type building blocks on the NHCs, including bicyclo[6.1.0]nonyne (BCN) and dibenzoazacyclooctyne (DBCO), allows for a broader array of azide-modified biomolecules to be employed. In this study, three new masked NHCs for the SPAAC Click reactions were synthesized and characterized. These SPAAC-modified NHCs successfully clicked and transformed their cyclooctynes into triazoles with organic azides at room temperature. The best NHC of the three was deposited onto gold electrode surfaces and successfully achieved coupling of redox-reporter-modified aptamer oligonucleotides, as verified via the electrochemical reduction of their reporter, methylene blue. While these results confirm the success of using cyclooctyne-based NHCs and azide-modified aptamers for copper-free SPAAC Click reactions, more research is needed to improve NHC packing to prevent the generation of hydrogen peroxide on gold during electrochemical interrogation of NBEs. Nevertheless, this study opens novel opportunities for surface modification with an expansive array of aptamers and, potentially, other biomolecules for electrochemical sensing applications.