Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O²⁻, type-I mechanism) or singlet oxygen (¹O₂*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT.

The way in which photons travel through biological tissues and subsequently become scattered or absorbed is a key limitation for traditional optical medical imaging techniques using visible light. In contrast, near-infrared wavelengths, in particular those above 1000 nm, penetrate deeper in tissues and undergo less scattering and cause less photo-damage, which describes the so-called “second biological transparency window”. Unfortunately, current dyes and imaging probes have severely limited absorption profiles at such long wavelengths, and molecular engineering of novel NIR-II dyes can be a tedious and unpredictable process, which limits access to this optical window and impedes further developments. Two-photon (2P) absorption not only provides convenient access to this window by doubling the absorption wavelength of dyes, but also increases the possible resolution. This review aims to provide an update on the available 2P instrumentation and 2P luminescent materials available for optical imaging in the NIR-II window.

Efficient photolabile protecting groups: how to achieve exceptional photo-triggered amino-acid delivery upon irradiation in the NIR.

Physical unclonable functions (PUFs) are artificial “fingerprints” provided by physical devices to authenticate manufactured goods. Their inherent unclonable nature positions them as one of the most promising tools to tackle global counterfeiting challenges. Leveraging the large parameter space in solution chemistry, chemically generated PUFs can achieve excellent device performance. Particularly, optically active materials have become valuable security inks thanks to their versatile, non‐invasive, and non‐destructive readouts, and PUF devices generated from stochastic nano‐/micro‐patterns of optical inks hold great potential. This review highlights recent advances in the design of optical PUF devices. A range of resonant and non‐resonant optical materials used as security taggants are presented and their incorporation in state‐of‐the‐art PUF devices is examined using non‐deterministic fabrication techniques. By outlining design criteria, challenges, and opportunities, a roadmap is provided for developing next‐generation PUFs using established and emerging optical probes and help advance security and reliability in anticounterfeiting technologies.

The synthesis of ethenylene-based periodic mesoporous organosilica nanoparticles for two-photon imaging and photodynamic therapy of breast cancer cells is described.