Photostable Organic Two-photon Dyes with Ultrahigh Brightness for Long-term Fluorescence Imaging.

Developing photostable two-photon dyes with high brightness and negligible photocytotoxicity is of key importance in fluorescence imaging but remains a huge challenge. Here, a two-photon dye with ultrahigh brightness and photostability is demonstrated for high-performance long-term two-photon fluorescence imaging. By terminated donor engineering, the designed DBD shows a higher two-photon absorption cross-section (δ, 418 GM vs 329 GM) and photoluminescence quantum yield (ΦPL , 62.74% vs 54.63%) than its counterpart DBA. As a consequence, two-photon fluorescence brightness (δ×ΦPL ) of DBD exhibits a 10-folded enhancement (262 GM vs 19 GM) in comparison with typical Coumarin 307 dye. More importantly, DBD displays ultrahigh photostability and negligible photobleaching under 10 min femtosecond laser irradiation, which stands in marked contrast to Coumarin 307. Furthermore, femtosecond transient absorption spectroscopy ascribes this ultrahigh photostability and negligible photobleaching to the inefficient intersystem crossing. With these merits, DBD can be used long-term two-photon fluorescence imaging in vitro.

Viscosity Effects on Excited-State Dynamics of Indocyanine Green for Phototheranostic.

The excited-state dynamics of indocyanine green (ICG) fundamentally determine its photophysical properties for phototheranostic. However, its dynamics are predictable to be susceptible toward intracellular viscosity due to its almost freely rotating structure, making the precise phototheranostic very challenging. Therefore, correlating the viscosity with the dynamics of ICG is of great importance and urgency for precise phototheranostic prospects. This study presents systemic investigations on the viscosity-dependent dynamics of ICG for phototheranostic. Femtosecond transient absorption (fs-TA) experiments elucidate a prolonged radiative transition (225 ps vs 152 ps) for ICG in a viscous environment, which benefits fluorescence. High viscosity remarkably extends the triplet excited-state lifetime of ICG but reduces its internal conversion (6.2 ps vs 2.2 ps). The extended triplet lifetime affords sufficient photosensitization time to enhance photodynamic therapy. A moderative internal conversion is unfavorable for heat production, resulting in inferior photothermal therapy. With this clear picture of excitation energy state dissipation in mind, we readily identified the safety laser power density for precise phototheranostic. This work provides an insightful understanding of viscosity-relevant excited-state dynamics toward phototheranostic, which is also beneficial for designing novel ICG derivatives with improved phototheranostic performance.

Chemiluminescent organic nanophotosensitizer for a penetration depth independent photodynamic therapy.

Photodynamic therapy initiated by external photoexcitation is a clinically-approved therapeutic paradigm, but its practical application has been severely hindered by the shallow penetration of light. Here, we describe a penetration-independent PDT modality using a chemiluminescent organic nanophotosensitizer, which is activated by hydrogen peroxide instead of external photoexcitation.

Water-soluble chiral CdSe/CdS dot/rod nanocrystals for two-photon fluorescence lifetime imaging and photodynamic therapy.

Compared with traditional organic contrast agents, semiconductor nanocrystals (NCs) have unique optical properties that are vital for biological applications with ultrahigh sensitivities, such as long fluorescence lifetime and large multiphoton absorption (MPA). However, the MPA properties and biological applications of chiral-ligand-stabilized semiconductor NCs have scarcely been reported, which seriously hinders their relevant applications. In this work, we report the aqueous phase transfer of CdSe/CdS dot/rod NCs with the use of cysteine molecules, after which the NCs preserve their high fluorescence quantum yield, long lifetime, and efficient circular dichroism. More importantly, the investigated dot/rod NCs show extremely large two- and three-photon absorption action cross-sections in the first and second biological windows, with maximum values of ∼21 000 GM at 800 nm and ∼4.6 × 10-78 cm6 s2 per photon2 at 1300 nm, which are among the largest values reported for water-soluble fluorescent nanoparticles. Interestingly, the dot/rod NCs exhibit a high singlet oxygen generation efficiency of 35%. In addition, for the first time, two-photon fluorescence lifetime imaging and photodynamic therapy of the dot/rod NCs were successfully demonstrated. The performed investigation of the optical properties of these water-soluble CdSe/CdS dot/rod NCs indicates that they are promising candidates for nonlinear biological imaging applications.

A small-molecule probe for ratiometric photoacoustic imaging of hydrogen sulfide in living mice.

A small-molecule photoacoustic probe based on cyanine dyes was developed by taking advantage of the nucleophilic substitution reaction of H2S with chlorine. The probe demonstrated specific response to H2S with ratiometric photoacoustic signals in the NIR region, which enabled real-time, accurate, high-resolution imaging of endogenous H2S in vivo.