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Directing nanoparticles to the nucleus by attachment of nuclear localization sequences (NLS) is an aim in many applications. Gold nanoparticles modified with two different NLS were studied while crossing barriers of intact cells, including uptake, endosomal escape, and nuclear translocation. By imaging of the nanoparticles and by characterization of their molecular interactions with surface-enhanced Raman scattering (SERS), it is shown that nuclear translocation strongly depends on the particular incubation conditions. After an 1 h of incubation followed by a 24 h chase time, 14 nm gold particles carrying an adenoviral NLS are localized in endosomes, in the cytoplasm, and in the nucleus of fibroblast cells. In contrast, the cells display no nanoparticles in the cytoplasm or nucleus when continuously incubated with the nanoparticles for 24 h. The ultrastructural and spectroscopic data indicate different processing of NLS-functionalized particles in endosomes compared to unmodified particles. NLS-functionalized nanoparticles form larger intraendosomal aggregates than unmodified gold nanoparticles. SERS spectra of cells with NLS-functionalized gold nanoparticles contain bands assigned to DNA and were clearly different from those with unmodified gold nanoparticles. The different processing in the presence of an NLS is influenced by a continuous exposure of the cells to nanoparticles and an ongoing nanoparticle uptake. This is supported by mass-spectrometry-based quantification that indicates enhanced uptake of NLS-functionalized nanoparticles compared to unmodified particles under the same conditions. The results contribute to the optimization of nanoparticle analysis in cells in a variety of applications, e.g., in theranostics, biotechnology, and bioanalytics.

The penetration of topically applied tacrolimus formulated in micelles into murine skin is reported, measured by X-ray microscopy. Tacrolimus and micelles are probed for the first time by this high spatial resolution technique by element-selective excitation in the C 1s- and O 1s-regimes. This method allows selective detection of the distribution and penetration depth of drugs and carrier molecules into biologic tissues. It is observed that small, but distinct quantities of the drug and micelles, acting as a drug carrier, penetrate the stratum corneum. A comparison is made with the paraffin-based commercial tacrolimus ointment Protopic®, where local drug concentrations show to be low. A slight increase in local drug concentration in the stratum corneum is observed, if tacrolimus is formulated in micelles, as compared to Protopic®. This underscores the importance of the drug formulations for effective drug delivery. Time-resolved penetration shows presence of drug in the stratum corneum 100 min after formulation application, with penetration to deeper skin layers at 1000 min. High resolution micrographs give indications for a penetration pathway along the lipid membranes between corneocytes, but also suggest that the compound may penetrate corneocytes.

The penetration of dexamethasone into human skin ex vivo is reported. X-ray microscopy is used for label-free probing of the drug and quantification of the local drug concentration with a spatial resolution reaching 70±5nm. This is accomplished by selective probing the dexamethasone by X-ray absorption. Varying the penetration time between 10min and 1000min provides detailed information on the penetration process. In addition, the stratum corneum has been damaged by tape-stripping in order to determine the importance of this barrier regarding temporally resolved drug penetration profiles. Dexamethasone concentrations distinctly vary, especially close to the border of the stratum corneum and the viable epidermis, where a local minimum in drug concentration is observed. Furthermore, near the basal membrane the drug concentration strongly drops. High spatial resolution studies along with a de-convolution procedure reveal the spatial distribution of dexamethasone in the interspaces between the corneocytes consisting of stratum corneum lipids. These results on local drug concentrations are interpreted in terms of barriers affecting the drug penetration in human skin.

Drugs that influence enzymes of lipid metabolism can cause pathological accumulation of lipids in animal cells. Here, gold nanoparticles, acting as nanosensors that deliver surface-enhanced Raman scattering (SERS) spectra from living cells provide molecular evidence of lipid accumulation in lysosomes after treatment of cultured cells with the three tricyclic antidepressants (TCA) desipramine, amitryptiline, and imipramine. The vibrational spectra elucidate to great detail and with very high sensitivity the composition of the drug-induced lipid accumulations, also observed in fixed samples by electron microscopy and X-ray nanotomography. The nanoprobes show that mostly sphingomyelin is accumulated in the lysosomes but also other lipids, in particular, cholesterol. The observation of sphingomyelin accumulation supports the impairment of the enzyme acid sphingomyelinase. The SERS data were analyzed by random forest based approaches, in particular, by minimal depth variable selection and surrogate minimal depth (SMD), shown here to be particularly useful machine learning tools for the analysis of the lipid signals that contribute only weakly to SERS spectra of cells. SMD is used for the identification of molecular colocalization and interactions of the drug molecules with lipid membranes and for discriminating between the biochemical effects of the three different TCA molecules, in agreement with their different activity. The spectra also indicate that the protein composition is significantly changed in cells treated with the drugs.

Label-free detection of core-multishell (CMS) nanocarriers and the anti-inflammatory drug dexamethasone is reported. Selective excitation by tunable soft X-rays in the O 1s-regime is used for probing either the CMS nanocarrier or the drug. Furthermore, the drug loading efficiency into CMS nanocarriers is determined by X-ray spectroscopy. The drug-loaded nanocarriers were topically applied to human skin explants providing insights into the penetration and drug release processes. It is shown that the core-multishell nanocarriers remain in the stratum corneum when applied for 100 min to 1000 min. Dexamethasone, if applied topically to human ex vivo skin explants using different formulations, shows a vehicle-dependent penetration behavior. Highest local drug concentrations are found in the stratum corneum as well as in the viable epidermis. If the drug is loaded to core-multishell nanocarriers, the concentration of the free drug is low in the stratum corneum and is enhanced in the viable epidermis as compared to other drug formulations. The present results provide insights into the penetration of drug nanocarriers as well as the mechanisms of controlled drug release from CMS nanocarriers in human skin. They are also compared to related work using dye-labeled nanocarriers and dyes that were used as model drugs.

Selective probing of dexamethasone in excised human skin using soft X-ray spectromicroscopy provides quantitative concentration profiles as well as two-dimensional drug distribution maps. Element- and site-selective excitation of dexamethasone at the oxygen K-edge with the lateral step width adjusted to 1 μm provides detailed information on the location of the drug in the different skin layers. The key of this work is to probe dexamethasone selectively at the carbonyl site (C3) by the O 1s → π* transition, providing also a most efficient way to quantify the drug concentration as a function of penetration depth in correlation with structural properties of the skin containing carboxyl and amide oxygen sites occurring at higher transition energy than dexamethasone. Following drug exposure for 4 h, the glucocorticoide is located in about equal amounts in the stratum corneum, the outermost horny layer of skin, and in the viable epidermis, whereas in the dermis no dexamethasone is detected. In the stratum corneum, most of the lipophilic drug is found in regions between corneocytes, where epidermal lipids are dominating.