Blending Low-Frequency Vibrations and Push–Pull Effects Affords Superior Photoacoustic Imaging Agents

Photoacoustic imaging (PAI), a state-of-the-art noninvasive in vivo imaging technique, has been widely used in clinical disease diagnosis. However, the design of high-performance PAI agents with three key characteristics, i.e., near-infrared (NIR) absorption (λ_abs>800 nm), intense PA signals, and excellent photostability, remains a challenging goal. Herein, we present a facile but effective approach for engineering PAI agents by amplifying intramolecular low-frequency vibrations and enhancing the push-pull effect. As a demonstration of this blended approach, we constructed a PAI agent ( BDP1-NEt₂ ) based on the boron-dipyrromethene (BODIPY) scaffold. Compared with indocyanine green (ICG, an FDA-approved organic dye widely utilized in PAI studies; λ_abs=788 nm), BDP1-NEt₂ exhibited a UV/Vis-NIR spectrum peaked at 825 nm, superior in vivo PA signal intensity and outstanding stability to offer improved tumor diagnostics. We believe this work provides a promising strategy to develop the next generation of PAI agents.     

Relaxation behavior of supra-molecular hydrogen-bonded liquid crystal phase structures: SA:11OBA

Low-frequency (20 Hz–10 MHz) dielectric response in liquid crystalline (LC) phases of hydrogen-bonded (HB) complex, SA:11OBA, is studied. Synthesis of SA:11OBA with non-mesogenic succinic acid (SA) and mesogenic p-n-undecyloxy benzoic acid (11OBA) and its spectroscopic confirmation are detailed. Phase transition temperatures (T_C) involving nematic, smectic-C (SmC), and smectic-G (SmG) phases by capacitance C(T) and loss tanΔ(T) anomaly agree with the microscopy (polarizing optical microscope) and calorimetry (differential scanning calorimetry) results. Low-frequency dispersion infers two types of reorientation processes, viz. higher frequency (～MHz) and lower frequency (kHz) processes. Distinct time scale mechanism are presented. Arrhenius behavior infers influence of HB on activation energy (E_a). Off-centered dispersion, viz. ?′(ω) with ?″(ω), analyzed through the Cole–Cole plots in N, SmC, and SmG phases infers a strong temperature trend for dielectric strength (Δ?) and distribution (α) parameters. Temperature dependence of α-parameter reveals on LC phases increasing fixture of molecular dipole in LC phase structure. Results are discussed in the wake of the body of data reported in LC phases exhibited by other LC compounds.     

凹筒型弯张式低频发射换能器

本文介绍了一种低频发射换能器,它结构上与Ⅰ型弯曲伸张换能器有相似之处,但呈凹筒形状,具有频率低、功率大、尺寸小、重量轻等诸多优点,且其独特的外型结构适合于组排基阵,有较好的应用前景。我们研制了大小两个该型换能器,其外型尺寸分别为φ186mm×330mm和φ130mm×250mm;谐振频率分别为855Hz和1050Hz;声源级分别为195.7dB和191.0dB。