Biosensors

Background: Brain temperature is an important determinant of neurological outcomes in ill infants, yet contributions of environmental temperature and cerebral blood flow remain uncovered because of the lack of non-invasive probes. Methods: Using non-invasive cot-side probes, we examined how cerebral blood flow influences brain temperature during mild cold stress induced by incubator-to-cot transfer. We studied 43 clinically stable infants in a tertiary neonatal intensive care unit. After cot transfer, infants were routinely fitted with knit caps and wrapped in cotton blankets. Scalp and superficial and deep brain temperatures were measured using infrared and zero-heat-flux thermometers, and superior vena cava (SVC) flow—a proxy for cerebral blood flow—was assessed using Doppler velocimetry before, immediately after, and 2 h after transfer, adjusting for rectal temperature. Results: Ambient temperature decreased from 29.7 (SD 0.8) °C to 26.8 (SD 0.9) °C, while rectal temperature remained stable. Scalp and brain temperatures declined after transfer but superficial and deep brain temperatures returned to baseline after 2 h of cap use. The regression coefficient between SVC flow and superficial brain temperature shifted from −0.176 (95% CI, −0.386 to 0.035) to 0.239 (−0.280 to 0.759) after transfer (difference: 0.415 [0.106 to 0.724]; p = 0.009), and then returned to baseline after 2 h (−0.079 [−0.528 to 0.372]). Conclusions: Relationships between brain temperature and perfusion were successfully monitored using non-invasive cot-side biosensors; cerebral blood flow appears to shift from facilitating heat dissipation in warm conditions to supporting heat delivery during cold stress. These findings underscore the physiological role of cerebral blood flow in maintaining brain temperature.

The sensitive detection of microRNA-21 (miR-21), a key biomarker for various cancers, is crucial for early diagnosis, yet conventional methods often face limitations in sensitivity and operational complexity. Here, we report a label-free biosensor based on a suspended graphene field-effect transistor (GFET) for the direct electrical detection of miR-21. The suspended architecture isolates the graphene channel from substrate-induced interference, resulting in enhanced carrier mobility and reduced electrical noise. After surface functionalization with a specific probe, the GFET demonstrated a clear concentration-dependent response to target miR-21. The binding events were transduced into a monotonic increase in relative resistance (ΔR/R₀) and a positive shift of the Dirac point (V_Dirac), achieving a detection limit in the femtomolar (fM) range. These results establish the suspended GFET as a highly sensitive and robust platform for quantifying nucleic acid biomarkers, holding significant potential for biomedical research and point-of-care diagnostics.

We report a highly sensitive and interference-free electrochemical sensor for dopamine (DA) detection in the presence of uric acid (UA) and ascorbic acid (AA), based on an in situ deposited graphitic carbon nitride (g-C₃N₄) and polymethyl thymol blue (PMTB) nanohybrid modified screen-printed carbon electrode (SPCE). The as-fabricated g-C₃N₄/PMTB/SPCE was thoroughly characterized using various physicochemical techniques. The electrochemical behavior of the modified electrode was systematically investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The g-C₃N₄/PMTB/SPCE exhibited excellent electrocatalytic activity toward the selective oxidation of DA under optimized experimental conditions, including pH and scan rate. Interference-free detection of DA in the presence of AA and UA was achieved using DPV and chronoamperometric methods, revealing a wide linear concentration range, an ultralow limit of detection, and high sensitivity. Furthermore, the practical applicability of the proposed sensor was validated by determining DA in artificial biofluid samples, including blood serum, and urine. The recovery results obtained good agreement with those obtained using high-performance liquid chromatography (HPLC), confirming the reliability and accuracy of the developed sensing platform.