Ultrasound defect sensitive mechanochromic material with blue-shifted emission for the detection of Cu2+ in Alzheimer's disease cells

Abstract

The mechanistic investigation and design of ultra-sensitive smart materials with multi-stimuli responsive properties are attracting much interest due to their utilization in several areas concurrently, such as mechanochromic and acidochromic materials, defect sensors, and chemosensors for analytes. Herein, the tailoring of an external stimuli-responsive novel coumarin-based luminogen (CFH) exhibiting green emission (λ_em = 515 nm) in the liquid state and red emission (λ_em = 698 nm) in the solid state opens up new avenues for the design of near-infrared emitting coumarin-based materials. CFH is an aggregation-induced enhanced emission (AIEE)-active material exhibiting solvatochromism and viscochromism. The weakly emissive crystals of CFH showed a relatively rare blue-shifted (48 nm) enhanced emission (3-fold) upon grinding. Fluorescence microscopy demonstrated that defect areas on the crystal surface become extremely emissive, indicating a “turn-on” defect-sensitive mechanochromism, susceptible to impact, friction, sculpting and ultrasonic vibrations. Solid CFH displayed acidochromic properties with extraordinary reversibility when exposed to trifluoroacetic acid (TFA)/triethylamine (TEA) vapour, displaying an on–off–on emission. Furthermore, CFH demonstrated “on–off” fluorescence responses to Cu²⁺ in water, exhibiting a detection limit (LOD) of 1.1 nM and Stern–Volmer constant (K_sv) of 2.84 × 10⁶ M⁻¹. The Job's plot and SC-XRD demonstrated a 1 : 1 binding stoichiometry for the CFH–Cu²⁺ complex. Leveraging this fluorescence response, portable test kit devices were developed for the detection of Cu²⁺. Bioimaging was carried out to examine the quenching of the probe with accumulated Cu²⁺ in SH-SY5Y model cells for neurodegenerative disorders compared to HEK-293 cells, suggesting that CFH can also be used for the intracellular sensing of Cu²⁺ in Alzheimer's disease (AD) cells.