Phototriggered targeting of nanocarriers for drug delivery

Stimuli-triggered targeting of drug delivery systems can both increase the therapeutic efficacy and lower toxicity by selectively delivering drugs at target sites with high specificity and efficiency. Light is a convenient and powerful stimulus for use in such drug delivery systems because it is readily available and noninvasive and offers excellent spatiotemporal control. The power and wavelength of light can be finely tuned for different photoresponsive systems to achieve efficient targeting at the tissue, cellular, or subcellular levels. Here, we have reviewed the various mechanisms for phototriggered targeting （phototargeting） of drug nanocarriers. We have discussed the three main phototargeting strategies： （1） targeting ligand activation; （2） particle size reduction; and （3） blood vessel disruption.

Mechanisms of photochemical release of dissolved organic matter and iron from resuspended sediments

Photochemical reactions can alter the transformation of sedimentary organic matter into dissolved organic matter(DOM)and affect its ultimate fate in water ecosystems.In the present study,the photorelease of DOM and Fe from resuspended lake sediments was investigated under different O_(2)and NO_(3)-concentration conditions to study the mechanisms of DOM and Fe photorelease.The amount of photoreleased Fe,which ranged from 0.22 to 0.70μmol/L,was significantly linearly correlated with the amount of photoreleased DOM.O_(2)and NO_(3)-could promote the photochemical release of DOM and Fe,especially during the initial 4 h irradiation.In general,the order of the photorelease rates of DOM and Fe under different conditions was as follows:NO_(3)-/aerobic>aerobic≈NO_(3)-/anaerobic>anaerobic.The photorelease rates of DOM and Fe were higher for the initial 4 hr irradiation than these for the subsequent 8 hr irradiation.The photorelease of DOM and Fe is thought to proceed via direct photodissolution and indirect processes.The relative contributions of indirect processes(>60%)was much greater than that of direct photodissolution(<40%).The photoproduced H 2 O_(2)under aerobic and anaerobic conditions indicated that hydroxyl radicals(·OH)are involved in the photorelease of DOM.Using·OH scavengers,it was found that 38.7%,53.7%,and 77.6%of photoreleased DOM was attributed to·OH under anaerobic,aerobic,and NO_(3)-/aerobic conditions,respectively.Our findings provide insights for understanding the mechanisms and the important role of·OH in the DOM and Fe photorelease from resuspended sediments.