Cryogenic electron microscopy (cryoEM) has become an indispensable technique for determining the structures of isolated biological macromolecules and imaging biomolecular structures within cells. While thin films of frozen-hydrated macromolecule suspensions can be directly prepared and imaged, these molecules must be extracted from their cellular context using existing sample preparation methods. On the other hand, cellular specimens preserve the native context, but the region of interest must be sectioned or subjected to focused ion-beam milling at cryogenic temperatures to achieve the necessary thickness for transmission electron imaging. Currently, no method exists for targeted cytoplasmic extraction of a subcellular volume from individual cells for direct vitrification and cryoEM imaging. In this study, a method is presented that addresses this gap. A system has developed that utilizes a force-sensitive microfluidic cantilever pipette to aspirate and dispense sample volumes as small as 204 fL onto conventional cryoEM sample supports, maintained at the dew point. This is followed by automatic vitrification for cryoEM imaging. Coupled with a fluorescence microscope, this setup allows for the extraction of a targeted subcellular volume from an individual cell and subsequent dispensing of the aspirated content onto an electron microscopy grid. A proof-of-concept is demonstrated by dispensing femtolitre volumes of the standard cryoEM single-particle sample, tobacco mosaic virus, and performing a subcellular biopsy from a single HeLa cell. Additionally, the challenges of manipulating such small volumes for cryoEM sample preparation are discussed, highlighting the current limitations of this approach and potential solutions for overcoming them.

This report introduces a novel optofluidic platform based on piezo-microelectromechanical systems (MEMS) technology, capable of identifying subtle variations in the fluid concentration. The system utilizes piezoelectric micromachined ultrasound transducers (PMUTs) as receivers to capture sound waves produced by nanosecond photoacoustic (PA) pulses emanating from a fluid target housed in PDMS microchannels. Additionally, a dedicated low-noise single-channel amplifier has been developed to extract the minute analog voltage signals from the PMUTs, given the inherently weak ultrasound signals generated by fluid targets. The PMUTs' proficiency in detecting changes in fluid concentration under both static and time-varying conditions has been documented and verified, confirming the platform's efficacy in monitoring fluid concentrations.

We report on the development of a novel piezo-MEMS-based optofluidic platform to detect the concentration of various species dissolved in a fluid. This platform employs piezoelectric micromachined ultrasound transducers (PMUTs) to work as a photoacoustic receiver, receiving ultrasound from fluid targets present in microfluidic channels while illuminated with a nanosecond pulsed laser. We fabricate both the PMUTs and the microfluidic channels and subsequently use them for the experiment. We also show the capability of PMUTs as a general photoacoustic receiver and demonstrate its signal-to-noise characteristics (31) and its wide fractional bandwidth (73%).