The rapid emergence of air-mediated diseases in a micro-climate demands on-site monitoring of airborne microparticles. The on-site detection of airborne microparticles becomes more challenging as the particles are highly localized and change dynamically over time. However, most existing monitoring systems rely on time-consuming sample collection and centralized off-site analysis. Here, we report a smartphone-based integrated microsystem for on-site collection and detection that enables real-time detection of indoor airborne microparticles with high sensitivity. The collection device, inspired by the Venturi effect, was designed to collect airborne microparticles without requiring an additional power supply. Our systematic analysis showed that the collection device was able to collect microparticles with consistent negative pressure, regardless of the particle concentration in the air sample. By incorporating a microfluidic-biochip based on inertial force to trap particles and an optoelectronic photodetector into a miniaturized device with a smartphone, we demonstrate real-time and sensitive detection of the collected airborne microparticles, such as Escherichia coli, Bacillus subtilis, Micrococcus luteus, and Staphylococcus with a particle-density dynamic range of 103-108 CFU mL-1. Because of its capabilities of minimal-power sample collection, high sensitivity, and rapid detection of airborne microparticles, this integrated platform can be readily adopted by the government and industrial sectors to monitor indoor air contamination and improve human healthcare.