This paper presents a low-cost, portable sensing platform for rapid DNA mass measurement, addressing a critical need in life science research. The platform features a novel interdigital open-gate junction field-effect transistor (ID-OGJFET) with a large sensing area that converts negatively charged DNA mass into an electrical current. The system enables DNA mass detection in under ten seconds with a resolution of less than 1 µA, demonstrating sensitivity across a range from 0.48 ng to 29.5 ng, achieving a Limit of Detection as low as 1.18-1.25 ng/µL. A custom-designed electronic reader and fluidic sample holder facilitate efficient operation. Simulation studies using molecular dynamics and finite element methods provide further insights into the sensor's DNA detection mechanism. This highly sensitive system is significantly more cost-effective than commercially available semiconductor characterization alternatives. The device's high performance and affordability make it a valuable tool for molecular biology applications, and it holds potential for advancing FET-based sensing instrumentation and measurement research.