Tumor-Microenvironment- Responsive Size-Shrinkable Drug-Delivery Nanosystems for Deepened Penetration Into Tumors

Over the years, the manipulation and clinical application of drug-delivery nanosystems for cancer diseases have attracted a rapid growth of academic research interests, and some nanodrugs have been approved for clinic application. Although encouraging achievements have been made, the potency of nanomedicines in cancer treatment is far from satisfaction, and one significant reason is the inefficient penetration of nanoparticles into solid tumors. Particle size is one of the most significant features that influence diffusion ability of the drug-delivery system in tumors. Size-shrinkable drug-delivery nanosystems possess a size-switchable property that can achieve passive targeting via the enhanced permeability and retention (EPR) effect and transform into ultrasmall particles in tumors for deep penetration into tumors. The tumor microenvironment is characterized by acidic pH, hypoxia, upregulated levels of enzymes, and a redox environment. In this review, we summarize and analyze the current research progresses and challenges in tumor microenvironment responsive size-shrinkable drug-delivery nanosystems. We further expect to present some meaningful proposals and enlightenments on promoting deep penetration into tumors of nanoparticles.

Pinned Luminescence Emission and Absorbance Band from Ultrasmall Ball-Milled Cd0.3Zn0.7Se Nanocrystals

We report the pinned absorbance and emission spectra of Cd0.3Zn0.7Se nanocrystals synthesized via mechanical alloying. The first emission peaks of Cd0.3Zn0.7Se nanocrystals milled for 5 and 10 h are observed at 3.36 eV, while the absorbance spectra of those milled for 10 and 20 h are observed at 4.47 eV. The emission peaks of nanocrystals milled for 5, 10, and 20 h have broad emissions centered at 2.90, 2.88, and 2.92 eV, respectively. Transmission electron microscopy histogram shows that each nanocrystal size distribution has a single population maxima of <2 nm. In addition, the center of each size distribution shifts toward the ultrasmall particles upon continuous milling. Particle sizes (d) of 0.73 nm are calculated from the first excitonic peaks of the pinned absorbance bands through the semiempirical sizing equation. The continuous reduction in particle sizes increases the surface-to-volume ratios of the nanocrystals. This increase eventually results in an increase in the surface states that translate into low photoluminescence intensity of pinned emission.