The correlation of mechanical properties of polymer materials with those of their molecular constituents is the foundation for their holistic comprehension and eventually for improved material designs and syntheses. Over the last decade, optical force probes (OFPs) were developed, shedding light on various unique mechanical behaviors of materials. The properties of polymers are diverse, ranging from soft hydrogels to ultra-tough composites, from purely elastic rubbers to viscous colloidal solutions, and from transparent glasses to super black dyed coatings. Only very recently, researchers started to develop tailored OFP solutions that account for such material requirements in energy (both light and force), in time, and in their spatially detectable resolution. We here highlight notable recent examples and identify future challenges in this emergent field.

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As ingle fluorescents ignal output often does not satisfy the detection accuracy requirements for bioactive compoundsi nbiological systems. It is of great interestt o develop ad ual-channel turn-on fluorescences ensing system for self-validated detection. Herein, we report as elf-quenching nanoparticle composed of dualt wo-photon dyes of naphthalimides, displaying almost no fluorescencea tb oth channels, owing to aggregation-caused quenching (ACQ). A dual two-photon-channel fluorescent probe for GSH was further developed by inserting ad isulfide bond between two naphthalimides. Upon treatment with GSH, the disulfide bond was cleaved, and two napthalimide fluorophores were separated, leadingt ot urn-on fluorescencea tb othc hannels. This dual-two-photon-channeld esign strategy can be easily extended to other analytes, simply by changing the linker molecules, which createsn ew opportunities to accurately monitorvariousbiological processes in living cells.