The article discusses the development and application of suspended microchannel resonators for weighing biomolecules, single cells, and nanoparticles in fluid. These resonators, designed to minimize viscous damping by surrounding the solution with a vacuum, achieve sub-femtogram resolution. The key innovation is the observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of the silicon crystal resonator, allowing for a six-orders-of-magnitude improvement in mass resolution over commercial quartz crystal microbalances. This technology enables applications such as mass-based flow cytometry, direct detection of pathogens, and non-optical sizing and mass density measurement of colloidal particles. The authors demonstrate the device's capability by measuring the binding of proteins and the mass of individual bacteria, showing potential for high-sensitivity and specific detection in various biological and medical contexts.The article discusses the development and application of suspended microchannel resonators for weighing biomolecules, single cells, and nanoparticles in fluid. These resonators, designed to minimize viscous damping by surrounding the solution with a vacuum, achieve sub-femtogram resolution. The key innovation is the observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of the silicon crystal resonator, allowing for a six-orders-of-magnitude improvement in mass resolution over commercial quartz crystal microbalances. This technology enables applications such as mass-based flow cytometry, direct detection of pathogens, and non-optical sizing and mass density measurement of colloidal particles. The authors demonstrate the device's capability by measuring the binding of proteins and the mass of individual bacteria, showing potential for high-sensitivity and specific detection in various biological and medical contexts.