A "turn-on" polymer nanothermometer based on aggregation induced emission for intracellular temperature sensing

Temperature measurements at the nanoscale facilitate the understanding of physiological processes related to heat in cells. Herein, we prepare a tetraphenylethylene-functionalized fluorophore (TPPEBr) with dual characteristics of twisted intramolecular charge transfer (TICT) and aggregation induced emission (AIE). It is polymerized with a thermo-responsive unit NIPAM to construct a fluorescent polymer nanothermometer (PNIPAM-TPPEBr). The phase transition behavior of PNIPAM from dispersed chains to dense spheres in aqueous media promotes the aggregation of TPPEBr fluorophores, which makes the fluorescence of PNIPAM-TPPEBr enhance with increasing temperature. Furthermore, the phase transition of PNIPAM is accompanied by a significant decrease in the polarity of the microenvironment, resulting in a blue shift in the emission wavelength of TPPEBr. Varying the ratio of NIPAM and TPPEBr can regulate the thermo-responsiveness of PNIPAM-TPPEBr in the physiological temperature range (31-38 °C), and the maximum relative thermal sensitivity reaches 13.2 % °C-1. The thermo-responsive performance of this nanothermometer is independent of the intracellular microenvironment, and it is successfully applied in the temperature imaging of A549 cells. Under the stimulation of ionomycin and oxidative phosphorylation inhibitor, the cell temperature increased by ca. 1.5 °C and ca. 1.0 °C, respectively.

Understanding Polyproline's Unusual Thermoresponsive Properties Using a Polyproline-Based Double Hydrophilic Block Copolymer

Polyproline is a unique thermoresponsive polymer characterized by large thermal and conformational hysteresis. This article employs polyproline-based double hydrophilic block copolymers (PNIPAMn-b-PLPm) to gain insight into polyproline's thermoresponsive mechanism. The amine-terminated poly(N-isopropylacrylamide) (NH2-PNIPAMm) was used as the macroinitiator for ring-opening polymerization of proline-NCA monomers, resulting in various block copolymers (PNIPAMn-b-PLPm) with varying PLP block lengths. Block copolymers' thermal phase transitions were compared with their homopolymer counterparts using turbidimetry, variable-temperature NMR, dynamic light scattering, and circular dichroism spectroscopy. These experiments revealed that regardless of their compositions, all block copolymers exhibited a two-stage collapse (TCP(PLP) > TCP(PNIPAM)) during the heating cycle. In contrast, only one clearing temperature (TCL) was observed during cooling. The observed clearing temperature is closely correlated to the clearing temperature of PNIPAM blocks, suggesting the role of water-soluble PNIPAM blocks in resolving the PLP blocks. Moreover, thermal and conformational hysteresis related to the polyproline block is significantly suppressed in the presence of a PNIPAM block. Linking PNIPAM blocks has two significant effects on PLP segments' thermoresponsive behavior. For example, during the heating cycle, the precollapsed PNIPAM chains (as TCP(PNIPAM) < TCP(PLP)) prevent orderly aggregation within the PLP block. Meanwhile, during the cooling cycle below the clearing temperature of the PNIPAM block, the PNIPAM chains impart water solubility (as TCL(PNIPAM) > TCL(PLP)) to the collapsed PLP chains. Overall, the PNIPAM block imparts water solubility and perturbs PLP chains to form the native aggregate structure, suppressing the hysteresis effect. Accordingly, the large thermal and conformational hysteresis associated with native PLP chains appears to result from a noninterfering aggregation above the critical temperature.

Thermoresponsive Property of Poly(N,N-bis(2-methoxyethyl)acrylamide) and Its Copolymers with Water-Soluble Poly(N,N-disubstituted acrylamide) Prepared Using Hydrosilylation-Promoted Group Transfer Polymerization

The group-transfer polymerization (GTP) of N,N-bis(2-methoxyethyl)acrylamide (MOEAm) initiated by Me2EtSiH in the hydrosilylation-promoted method and by silylketene acetal (SKA) in the conventional method proceeded in a controlled/living manner to provide poly(N,N-bis(2-methoxyethyl)acrylamide) (PMOEAm) and PMOEAm with the SKA residue at the α-chain end (MCIP-PMOEAm), respectively. PMOEAm-b-poly(N,N-dimethylacrylamide) (PDMAm) and PMOEAm-s-PDMAm and PMOEAm-b-poly(N,N-bis(2-ethoxyethyl)acrylamide) (PEOEAm) and PMOEAm-s-PEOEAm were synthesized by the block and random group-transfer copolymerization of MOEAm and N,N-dimethylacrylamide or N,N-bis(2-ethoxyethyl)acrylamide. The homo- and copolymer structures affected the thermoresponsive properties; the cloud point temperature (Tcp) increasing by decreasing the degree of polymerization (x). The chain-end group in PMOEAm affected the Tcp with PMOEAmx > MCIP-PMOEAmx. The Tcp of statistical copolymers was higher than that of block copolymers, with PMOEAmx-s-PDMAmy > PMOEAmx-b-PDMAmy and PMOEAmx-s-PEOEAmy > PMOEAmx-b-PEOEAmy.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Fluorescent and stimuli-responsive performance of polymer composites filled with tetraphenylethene derivatives

In this study, a series of tetraphenylethene (TPE) derivatives with 3-butenloxy moieties were synthesized. The developed TPE with different number of substituent groups showed controlled aggregation-induced emission performance and variable...