Digital microfluidics (DMF) is a promising technique for carrying out miniaturized, automated biochemical assays in which discrete droplets of reagents are actuated on the surface of an array of electrodes. A limitation for DMF is nonspecific protein adsorption to device surfaces, which interferes with assay fidelity and can cause droplets to become unmovable. Here, we report the results of a quantitative analysis of protein adsorption on DMF devices by means of confocal microscopy and secondary ion mass spectrometry. This study led us to a simple and effective method for limiting the extent of protein adsorption: the use of low concentrations of Pluronic F127 as a solution additive. This strategy has a transformative effect on digital microfluidics, facilitating the actuation of droplets containing greater than 1000-fold higher protein concentrations than is possible without the additive. To illustrate the benefits of this new method, we implemented a DMF-driven protein digest assay using large concentrations (1 mg/mL) of protein-substrate. The use of Pluronic additives solves a sticky problem in DMF, which greatly expands the range of applications that are compatible with this promising technology.

SUMMARY TRPA1 and TRPV1 are crucial pain mediators, but how their interaction contributes to persistent pain is unknown. Here, we identify Tmem100 as a potentiating modulator of TRPA1-V1 complexes. Tmem100 is co-expressed and forms a complex with TRPA1 and TRPV1 in DRG neurons. Tmem100-deficient mice show a reduction in inflammatory mechanical hyperalgesia and TRPA1- but not TRPV1-mediated pain. Single-channel recording in a heterologous system reveals that Tmem100 selectively potentiates TRPA1 activity in a TRPV1-dependent manner. Mechanistically, Tmem100 weakens the association of TRPA1 and TRPV1, thereby releasing the inhibition of TRPA1 by TRPV1. A Tmem100 mutant, Tmem100-3Q, exerts the opposite effect, i.e., it enhances the association of TRPA1 and TRPV1 and strongly inhibits TRPA1. Strikingly, a cell-permeable peptide (CPP) containing the C-terminal sequence of Tmem100-3Q mimics its effect and inhibits persistent pain. Our study unveils a context-dependent modulation of the TRPA1-V1 complex, and Tmem100-3Q CPP is a promising pain therapy.

Superresolution fluorescence microscopy overcomes the diffraction resolution barrier and allows the molecular intricacies of life to be revealed with greatly enhanced detail. However, many current superresolution techniques still face limitations and their implementation is typically associated with a steep learning curve. Patterned illumination-based superresolution techniques [e.g., stimulated emission depletion (STED), reversible optically-linear fluorescence transitions (RESOLFT), and saturated structured illumination microscopy (SSIM)] require specialized equipment, whereas single-molecule-based approaches [e.g., stochastic optical reconstruction microscopy (STORM), photo-activation localization microscopy (PALM), and fluorescence-PALM (F-PALM)] involve repetitive single-molecule localization, which requires its own set of expertise and is also temporally demanding. Here we present a superresolution fluorescence imaging method, photochromic stochastic optical fluctuation imaging (pcSOFI). In this method, irradiating a reversibly photoswitching fluorescent protein at an appropriate wavelength produces robust single-molecule intensity fluctuations, from which a superresolution picture can be extracted by a statistical analysis of the fluctuations in each pixel as a function of time, as previously demonstrated in SOFI. This method, which uses off-the-shelf equipment, genetically encodable labels, and simple and rapid data acquisition, is capable of providing two-to threefold-enhanced spatial resolution, significant background rejection, markedly improved contrast, and favorable temporal resolution in living cells. Furthermore, both 3D and multicolor imaging are readily achievable. Because of its ease of use and high performance, we anticipate that pcSOFI will prove an attractive approach for superresolution imaging.subdiffraction-limit | two-color imaging | membrane rafts F luorescence imaging has become one of the major avenues for analyzing various molecular events underlying cellular processes. Even though many fluorophores can be used as molecular labels, direct observation at the molecular length scale is hampered by the diffraction of light. To provide a more detailed image of molecular events in cells, a number of techniques have been recently developed that bestow far-field fluorescence microscopy with fundamentally unlimited spatial resolution (1, 2). These techniques, either based on patterned illumination [such as stimulated emission depletion (STED) microscopy (3, 4), reversible optically linear fluorescence transitions (RESOLFT) microscopy (5), and saturated structured illumination microscopy (SSIM) (6)] or repeated single-molecule localization [such as photo-activation localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM), fluorescence-PALM (F-PALM), ground-state depletion microscopy (GSDIM) microscopy (7-10)], are capable of improving spatial resolution by over an order of magnitude. However, these methods still face limitations. STED, RESOLFT, and SSIM microscopy ...

Compartmentalized biochemical activities are essential to all cellular processes, but there is no generalizable method to visualize dynamic protein activities in living cells at a resolution commensurate with their compartmentalization. Here we introduce a new class of fluorescent biosensors that detect biochemical activities in living cells at a resolution up to three-fold better than the diffraction limit. Utilizing specific, binding-induced changes in protein fluorescence dynamics, these biosensors translate kinase activities or protein-protein interactions into changes in fluorescence fluctuations, which are quantifiable through stochastic optical fluctuation imaging. A Protein Kinase A (PKA) biosensor allowed us to resolve minute PKA activity microdomains on the plasma membrane of living cells and uncover the role of clustered anchoring proteins in organizing these activity microdomains. Together, these findings suggest that biochemical activities of the cell are spatially organized into an activity architecture, whose structural and functional characteristics can be revealed by these new biosensors.

We have developed a versatile new class of genetically encoded fluorescent biosensor based on reversible exchange of the heterodimeric partners of green and red dimerization dependent fluorescent proteins (ddFPs). This strategy has been used to construct both intermolecular and intramolecular ratiometric biosensors for qualitative imaging of caspase activity, Ca2+ concentration dynamics, and other second messenger signaling activities.