Smart Pellet System: Autonomous Colorimetric Diagnostics in Unprocessed Biological Waste for Low-Resource and Space Environments

Abstract

The absence of passive, equipment-free diagnostic platforms capable of operating directly within unprocessed biological waste represents a fundamental barrier to early disease detection in resource-limited and non-terrestrial environments. We propose the Smart Pellet System, a conceptual seven-pellet colorimetric diagnostic platform in which each 3-5 mm microreactor autonomously detects one clinically significant urinary or fecal biomarker - glucose (diabetes mellitus), microalbumin (chronic kidney disease), bilirubin (hepatic dysfunction), fecal hemoglobin (colorectal cancer), heme fragments (occult bleeding), fecal bile acids (pancreatic cancer),

and NMP22 (bladder cancer) - through an integrated six-layer architecture combining L-aptamer molecular gating, nanoporous organosilica filtration, molecularly imprinted polymer recognition, enzyme-nanozyme catalytic amplification, and spatially segregated chromogenic microdomains. Each pellet is externally coated with an iron oxide pigment whose color precisely matches its internal diagnostic colorimetric output, enabling simultaneous user identification and automated optical sensor recognition. L-aptamers immobilized on the pellet surface maintain gate closure in toilet water, protecting enzymatic components from aqueous degradation, and open selectively upon target biomarker binding. Dilution-corrected theoretical modeling confirms that pathological concentrations of all seven biomarkers remain detectable following the approximately 27-fold dilution imposed by household toilet water, with colorimetric responses predicted within 3-18 minutes. The gravity-independent diffusion mechanism renders the system uniquely applicable to space medicine environments where conventional diagnostic platforms cannot operate. This work additionally presents the Smart Pellet Dispenser, a compact cistern-mounted automated device (10 × 4 × 3 cm) that stores all pellets in a dry reservoir and selectively releases one pellet per flush cycle through an integrated optical recognition module (TCS34725 RGB sensor) and a flush-driven hydraulic ratchet mechanism, enforcing a programmed seven-day diagnostic rotation without user intervention. Together, the Smart Pellet System and Smart Pellet Dispenser establish the complete engineering foundation for a passive, continuous, multi-disease surveillance platform applicable to both low-resource terrestrial communities and future long-duration space exploration missions.