No abstract

Nonspecific interactions of conjugated polymers (CPs) with various proteins prove to be a major impediment for researchers when designing a suitable CP-based probe for the amplified and selective recognition of particular proteins in complex body fluids. Herein, a new strategy is presented for the precise and specific monitoring of clinically important serum albumin (SA) proteins at the nanomolar level using fluorescence resonance energy transfer (FRET)-modulated CP–surfactant ensembles as superior sensing materials. In brief, the newly designed color-tunable CP PF–DBT–Im undergoes intense aggregation with the surfactant sodium dodecyl sulfate (SDS), enabling drastic change in the emission color from violet to deep red due to intermolecular FRET. The emission of PF–DBT–Im/SDS ensembles then changed from deep red to magenta specifically on addition of SAs owing to the exclusive reverse FRET facilitated by synergistic effects of electrostatic interactions, hydrophobic forces, and the comparatively high intrinsic quantum yield of SAs. Interestingly, PF–DBT–Im itself could not differentiate SAs from other proteins, demonstrating the superiority of the PF–DBT–Im/SDS self-assembly over PF–DBT–Im. Finally, an affordable smartphone-integrated point-of-care (PoC) device is also fabricated as a proof-of-concept for the on-site and rapid monitoring of SAs, validating the potential of the system in long-term clinical applications.

Among several detection techniques, fluorescence based optical sensors are regarded as superior owing to distinct features like simplicity, remarkable sensitivity and prompt signal response time. Signal amplification remains most effective strategy to further boost the performance of such sensors. Thanks to the unique light–harvesting and energy transfer properties of conjugated polymers (CPs) which make them as promising and key candidates for achieving proficient sensing through amplified fluorescence signal. Owing to such remarkable properties, past decade has witnessed numerous CPs based optical sensors and devices for monitoring of various species. In this review, we first introduce CPs and highlight their exclusive characteristics. Then, the superiority of CPs over small molecule based sensors has been demonstrated along with thorough discussion on underlying sensing mechanism. Afterwards, it is described how solid state sensing using CPs dominates over solution based sensing in terms of sensitivity. Later on, CP-amplified fluorescence detection of some explosives, pollutants, biomarker etc. on solid support has been summarized by shedding light on some recent representative papers. Finally, the current challenges and future prospective for advancement of the respective research area has been discussed.

Photochromic indolylfulgimides covalently attached to polymers have beneficial properties for optical switching. A 3-indolylfulgide and two 3-indolylfulgimides with one or two polymerizable styrene groups attached on the nitrogen atom(s) were synthesized. Copolymerization with methyl methacrylate (MMA) provided linear copolymers (one styrene group) or a cross-linked copolymer (two styrene groups). The properties of the monomers and copolymers in toluene or as thin films were characterized. The new copolymers were photochromic (reversible Z-to-C isomerization), absorbed visible light, and revealed good thermal and photochemical stability. At room temperature, all copolymer films showed no loss of absorbance after 5 weeks. At 80 °C in either toluene or as films, the Z-forms copolymers were less stable than the C-form copolymers, which showed little or no degradation after 400 h. The degradation rate due to repeated ring-closing – ring opening cycles was less than 3% per 100 cycles. The cross-linked copolymer showed photochemical stability comparable to monomeric fulgides in toluene, <1% per 100 cycles. In general, the properties of the linear and cross-linked copolymers were similar to the corresponding monomers in toluene. In films, the conformations of the Z-form were restricted due to the matrix indicating that the preparation of films from the C-form is advantageous.

High hydrophobicity of 𝝅-extended conjugated polymers (CPs) adversely affects their photoluminescence quantum yield (PLQY) in water and hydrogel/solid state via an unsolicited aggregation-caused quenching (ACQ) process which ultimately hampers their sensing and imaging performance. Herein, an efficient strategy is presented to suppress and transform such ACQ process into an encapsulation-induced emission enhancement (EIEE) effect through facile preparation of CP/Pluronic F-127 fluorescent hybrid micelles and hydrogel. As a proof-of-concept, successful encapsulation of polyfluorene derivative PF-DBT-Im into F-127 micelles not only displays an improved PLQY (≈200% increment) in water/hydrogel state but also delivers unique and augmented sensing responses toward the emerging pollutants tetracyclines taken as model analyte, validating the superiority of EIEE-active hybrid micellar systems over ACQ suffering PF-DBT-Im aggregates. The established method not only provides a facile solution to circumvent ACQ problem existing in low water dispersible CPs but also endorses an enhanced, simplified sensing system for visual and on-site detection of analytes with likely futuristic applications in biomedicine and solid-state optoelectronics.