Boosting Luminescence Efficiency of Near-Infrared-II Aggregation-Induced Emission Luminogens via a Mash-Up Strategy of π-Extension and Deuteration for Dual-Model Image-Guided Surgery

The simultaneous pursuit of accelerative radiative and restricted nonradiative decay is of tremendous significance to construct high-luminescence-efficiency fluorophores in the second near-infrared wavelength window (NIR-II), which is seriously hindered by the energy gap laws. Herein, a mash-up strategy of π-extension and deuteration is proposed to efficaciously ameliorate the knotty problem. By extending the π-conjugation of the aromatic fragment and introducing an isotope effect to the aggregation-induced emission luminogen (AIEgen), an improved oscillator strength (f), coupled with suppressed deformation and high-frequency oscillation in the excited state, are successively implemented. In this case, a faster rate of radiative decay (kr) and restricted nonradiative decay (knr) are simultaneously achieved. Moreover, the preeminent emissive property of AIEgen in the molecular state could be commendably inherited by the aggregates. The corresponding NIR-II emissive AIEgen-based nanoparticles display high brightness, large Stokes shift, and superior photostability simultaneously, which can be applied for image-guided cancer and sentinel lymph node (SLN) surgery. This work thus provides a rational roadmap to improve the luminescence efficiency of NIR-II fluorophores for biomedical applications.

Ligand-Dependent Intramolecular Motion of Native Nicotinic Acetylcholine Receptors Determined in Living Myotube Cells via Diffracted X-ray Tracking

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that play an important role in signal transduction at the neuromuscular junction (NMJ). Movement of the nAChR extracellular domain following agonist binding induces conformational changes in the extracellular domain, which in turn affects the transmembrane domain and opens the ion channel. It is known that the surrounding environment, such as the presence of specific lipids and proteins, affects nAChR function. Diffracted X-ray tracking (DXT) facilitates measurement of the intermolecular motions of receptors on the cell membranes of living cells, including all the components involved in receptor function. In this study, the intramolecular motion of the extracellular domain of native nAChR proteins in living myotube cells was analyzed using DXT for the first time. We revealed that the motion of the extracellular domain in the presence of an agonist (e.g., carbamylcholine, CCh) was restricted by an antagonist (i.e., alpha-bungarotoxin, BGT).

Semiconducting Polymer Nanoparticles with Intramolecular Motion-Induced Photothermy for Tumor Phototheranostics and Tooth Root Canal Therapy

Much effort is devoted to develop agents with superior photoacoustic/photothermal properties for improved disease diagnosis and treatment. Herein, a new fused two isoindigo (DIID)-based semiconducting conjugated polymer (named PBDT-DIID) is rationally designed and synthesized with a strong near-infrared absorption band ranging from 700 to 1000 nm. Water-dispersing nanoparticles (NPs) of PBDT-DIID are prepared with good biocompatibility and a rather high photothermal conversion efficiency (70.6%), as the active excited-state intramolecular twist around the central double bonds in DIID permits most of the absorbed excitation energy flow to heat deactivation pathway through internal conversion. The photoacoustic signal can be further magnified by incorporation of polylactide (PLA) in the NP core to confine the generated heat of PBDT-DIID within NPs. The resultant doped NPs show excellent performance in photoacoustic imaging-guided photothermal therapy in an orthotopic 4T1 breast tumor-bearing mouse model. It is also found that the photothermal effect of the PBDT-DIID NPs is safe and quite efficacious to highly improve the root canal treatment outcome by heating the 1% NaClO solution inside the root canal upon 808 nm laser irradiation in a human extracted tooth root canal infection model.

Evoking Highly Immunogenic Ferroptosis Aided by Intramolecular Motion-Induced Photo-Hyperthermia for Cancer Therapy

Immunogenic cell death (ICD) through apoptosis or necroptosis is widely adopted to improve the therapeutic effect in cancer treatment by triggering a specific antitumor immunity. However, the tumor resistance to apoptosis/necroptosis seriously impedes the therapeutic effect. Recently, ferroptosis featured with excessive lipid peroxidation is demonstrated capable of bypassing the apoptosis/necroptosis resistance to kill cancer cells. To date, numerous efficient ferroptosis inducers are developed and successfully utilized for sensitizing cancer cells to ferroptosis. Unfortunately, these inducers can hardly generate adequate immunogenicity during induction of ferroptotic cancer cell death, which distinctly attenuates the efficacy of triggering antitumor immune response, therefore leads to unsatisfactory therapeutic effect. Herein, a novel high-performance photothermal nanoparticle (TPA-NDTA NP) is designed by exploiting energy via excited-state intramolecular motion and employed for immensely assisting ferroptosis inducer to evoke highly efficient ICD through ferroptosis pathway. Tumor models with poor immunogenicity are used to demonstrate the tremendously enhanced therapeutic effect endowed by highly enhanced immunogenic ferroptosis in vitro and in vivo by virtue of the NPs. This study sheds new light on a previously unrecognized facet of boosting the immunogenicity of ferroptosis for achieving satisfactory therapeutic effect in cancer therapy.

A Class of Biocompatible Dye-Protein Complex Optical Nanoprobes

Molecular organic dyes are classic fluorescent nanoprobes finding tremendous uses in biological and life sciences. Yet, they suffer from low brightness, poor photostability, and lack of functional groups for bioconjugation. Here, we describe a class of biocompatible dye-protein optical nanoprobes, which show long-time photostability, superbrightness, and enriched functional groups. These nanoprobes utilize apoferritin (an intracellular protein for iron stores and release) to encase appropriate molecular organic dyes to produce on-demand fluorescence in aqueous solution. A pH-driven dissociation-reconstitution process of apoferritin subunits allows substantial incorporation of hydrophilic (aggregation caused quenching, ACQ) or hydrophobic (aggregation induced enhancement, AIE) dye molecules into the protein nanocavity (8 nm), producing monodispersed dye-apoferritin nanoparticles (apo-dye-NPs, ∼12 nm). As compared with single dye monomer, single apo-dye-NPs possess hundreds of times larger molar extinction coefficient and 2 orders of magnitude higher absolute luminescence quantum yield (up to 45-fold), multiplying fluorescence brightness up to 2778-fold. We show that varying the type of incorporated dyes entails a precise control over nanoprobe emission profile tunable in a broad spectral range of 370-1300 nm. Mechanical investigations indicate that the diversified microstructures of nanocavity inner surface are able to conform ACQ dyes at reasonable space interval while providing protein-guided-stacking for AIE dyes, thus enhancing fluorescence quantum yield through confining intermolecular quenching and intramolecular rotation. Moreover, apo-dye-NPs are able to emit stable fluorescence (over 13 min) without quenching in confocal imaging of HepG2 cancer cell under ultrahigh laser irradiance (1.3 × 10⁶ W/cm²). These superb properties make them suitable, as demonstrated in this work, for long-term super-resolved structured illumination microscopic cell imaging (spatial resolution, 117 nm) over 48 h, near-infrared (NIR) fluorescence angiography imaging of whole-body blood vessels (spatial resolution, 380 μm), and NIR photoacoustic imaging of liver in vivo.

A Borondifluoride-Complex-Based Photothermal Agent with an 80 % Photothermal Conversion Efficiency for Photothermal Therapy in the NIR-II Window

Small organic photothermal agents (SOPTAs) that absorb in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable in photothermal therapy for their good biocompatibility and deeper tissue penetration. However, the design of NIR-II absorbing SOPTAs remains a great challenge. Herein, we report that molecular engineering of BF₂ complex via strengthening the donor-acceptor conjugation and increasing the intramolecular motions is an efficient strategy to achieve NIR-II absorbing SOPTAs with high photothermal performance. Based on this strategy, a BF₂ complex, BAF4, was designed and synthesized. BAF4 exhibits an intense absorption maximum at 1000 nm and negligible fluorescence. Notably, the nanoparticles of BAF4 achieve a high photothermal conversion efficiency value of 80 % under 1064 nm laser irradiation (0.75 W cm^-2 ). In vitro and in vivo studies reveal the great potential of BAF4 nanoparticles in photoacoustic imaging-guided photothermal therapy in the NIR-II window.

Boosting Photoacoustic Effect via Intramolecular Motions Amplifying Thermal-to-Acoustic Conversion Efficiency for Adaptive Image-Guided Cancer Surgery

Photoacoustic (PA) imaging emerges as a promising technique for biomedical applications. The development of new strategies to boost PA conversion without depressing other properties (e.g., fluorescence) is highly desirable for multifunctional imaging but difficult to realize. Here, we report a new phenomenon that active intramolecular motions could promote PA signal by specifically increasing thermal-to-acoustic conversion efficiency. The compound with intense intramolecular motion exhibits amplified PA signal by elevating thermal-to-acoustic conversion, and the fluorescence also increases due to aggregation-induced emission signature. The simultaneously high PA and fluorescence brightness of TPA-TQ3 NPs enable precise image-guided surgery. The preoperative fluorescence and PA imaging are capable of locating orthotopic breast tumor in a high-contrast manner, and the intraoperative fluorescence imaging delineates tiny residual tumors. This study highlights a new design guideline of intramolecular motion amplifying PA effect.