Methylated cytosine is proved to have an important role as an epigenetic signal in gene regulation and is often referred to "the fifth base of DNA". A comprehensive understanding of the electronic excited state relaxation in cytosine and its methylated derivatives is crucial for revealing UV-induced photodamage to the biological genome. Because of the existence of multiple closely lying "bright" and "dark" excited states, the decay pathways in these DNA nucleosides are the most complex and the least understood so far. In this study, femtosecond transient absorption with different excitation wavelengths (240-296 nm) was used to study the relaxation of excited electronic states of 5-methylcytosine (5mC) and 2'-deoxy-5-methylcytidine (5mdCyd) in phosphate buffered aqueous solution and in acetonitrile solution. Two distinct nonradiative decay channels were directly observed. The first one is a several picosecond internal conversion channel that involves two bright ππ* states (ππ* and ππ*) when ππ* state is initially populated. The second channel contains the lower energy ππ* state and a so far experimental unidentified long-lived state which exhibits a several nanosecond lifetime. The long-lived state can only be accessed by the initially excited ππ* state. Inspired by this new discovery in 5mC and 5mdCyd, we revisited the decay of excited state of 2'-deoxycytidine (dCyd), revealing very similar decay pathways. Additionally, a well-known dark nπ* state (carbonyl lone pair) with ∼30 ps lifetime is present in both decay channels in dCyd. With our detailed experimental results, we successfully reconcile the long history debate of cytosine excited state relaxation mechanism by pointing out that the reason for the complex dynamics under traditional 266 nm excitation is mixed signals from the above-mentioned two distinct decay pathways. Our findings lead to a dramatically different and new picture of electronic energy relaxation in 5mdCyd/dCyd and could help to understand photostability as well as UV-induced photodamage of these nucleotides and related DNAs.

Engineering near-infrared (NIR) light-sensitive enzymes remains a huge challenge. A photothermal effect-associated method is developed for tailoring the enzymatic activity of enzymes by exposure to NIR light. An ultrasmall platinum nanoparticle was anchored in an enzyme to generate local heating upon NIR irradiation, which enhanced the enzyme activity without increasing bulk temperature. Following NIR irradiation, the enzyme activity was tailored rapidly and reversibly, and was modulated by varying laser power density and irradiation time. Four enzymes were engineered, including glucoamylase, glucose oxidase, catalase, and proteinase K with NIR-light sensitivity, and demonstrated their utility in practical applications such as photolithography and NIR light-responsive antibacterial or anticancer actions. Our investigation suggests that this approach could be broadly used to engineer enzymes with NIR-light sensitivity for many biological applications.

Engineering near-infrared (NIR) light-sensitive enzymes remains ah uge challenge.Aphotothermal effectassociated method is developed for tailoring the enzymatic activity of enzymes by exposure to NIR light. An ultrasmall platinum nanoparticle was anchored in an enzyme to generate local heating upon NIR irradiation, which enhanced the enzyme activity without increasing bulk temperature.F ollowing NIR irradiation, the enzyme activity was tailored rapidly and reversibly,a nd was modulated by varying laser power density and irradiation time.F our enzymes were engineered, including glucoamylase,g lucose oxidase,c atalase,a nd proteinase Kwith NIR-light sensitivity,and demonstrated their utility in practical applications such as photolithography and NIR light-responsive antibacterial or anticancer actions.Our investigation suggests that this approach could be broadly used to engineer enzymes with NIR-light sensitivity for many biological applications.

We numerically studied the optical properties of spherical nanostructures made of an emitter core coated by a silver shell through the generalized Mie theory. When there is a strong coupling between the localized surface plasmon in the metallic shell and the emitter exciton in the core, the extinction spectra exhibit two peaks. Upon adsorption of analytes on these core-shell nanostructures, the intensities of the two peaks change with opposite trends. This property makes them potential sensitive ratiometric sensors. Molecule adsorption on these nanostructures can be quantified through a very simple optical configuration likely resulting in a much faster acquisition time compared with systems based on the traditional metal nanoparticle surface plasmon resonance (SPR) biosensors.

Over the last century, quantum theories have revolutionized our understanding of material properties. One of the most striking quantum phenomena occurring in heterogeneous media is the quantum tunneling effect, where carriers can tunnel through potential barriers even if the barrier height exceeds the carrier energy. Interestingly, the tunneling process can be accompanied by absorption or emission of light. In most tunneling junctions made of noble metal electrodes these optical phenomena are governed by plasmonic modes, i.e. light-driven collective oscillations of surface electrons. In the emission process, plasmon excitation via inelastic tunneling electrons can improve the efficiency of photon generation resulting in bright nanoscale optical sources. On the other hand, the incident light can affect the tunneling behavior of plasmonic junctions as well, leading to phenomena such as optical rectification and induced photocurrent. Thus, plasmonic tunneling junctions provide a rich platform for investigating light-matter interactions paving the way for various applications, including nanoscale light sources, sensors, and chemical reactors. In this paper, we will introduce recent research progresses and promising applications based on the plasmonic tunneling junctions.