Advances in nanotechnology have prompted rapid progress and versatile imaging modalities for diagnostics and treatment of diseases. Molecular imaging is a powerful technique for quantifying physiological changes in vivo using noninvasive imaging probes. These probes are used to image specific cells and tissues within a whole organism. Currently, imaging is an essential part of clinical protocols providing morphological, structural, metabolic and functional information. Using theranostic micro- or nanoparticles, which combine both therapeutic and diagnostic capabilities in one single entity, holds a true promise to propel the biomedical field toward personalized medicine. With this approach, biological processes can be directly and simultaneously monitored with the treatment of the diseases. This mini-review highlights the recent innovative diagnostic imaging aspects of porous silicon (PSi) materials and emphasizes their potential as theranostic platforms and tools for the clinic. Multiple biomedical imaging applications of the PSi materials are also outlined.

The engineering of well-defined micro- and nanoscaled surface topographies on biomedical metals and polymeric materials has been explored as a strategy to control biological responses. In this review, the ability of surface features engineered by a variety of methods to promote or reduce protein, blood, and bacterial adhesion is discussed independent of surface chemistry. The interaction of proteins with surface topography is fundamentally important and influences the conformation, the types of protein, as well as the overall amount of protein adhesion, which in many instances is increased over the associated increase in surface area. The use of superhydrophobic surface features is discussed as a manner to engineer antifouling surfaces with protein, blood, and bacterial resistance.

The highly specific functions of DNA can be used for designing novel functional materials. However, aqueous solubility and biochemical instability of DNA impede its direct utilization as a functional component. Herein, preparation of a hybrid material encapsulating the DNA molecules (double-stranded salmon sperm, 50–5000 base pairs) in robust host—sol–gel-derived silica—has been described. The encapsulation was carried out in two steps: hydrolysis of an acidic tetraethylorthosilicate [Si(OC2H5)4] sol and was followed by condensation near physiological pH upon addition of alkaline DNA-containing solutions. The gelation behavior and structural properties of the DNA–silica hybrids were investigated by 29Si nuclear magnetic resonance and by nitrogen adsorption. The selective adsorption of a DNA-interactive reagent molecule (ethidium bromide) in their diluted aqueous solutions on DNA–silica hybrids confirmed that the DNA molecules remained entrapped within the silica host without any deterioration. A DNA encapsulation mechanism correlating the silica microstructure and DNA holding efficiency has been proposed.

In this study, silicon nanowire (SiNW)/polycaprolactone composites with different surface topographies were fabricated by straightforward embedding or printing methods and their cytocompatibility was evaluated with a bone-relevant cell line derived from mouse stroma. The incorporation of biocompatible polymers with semiconducting SiNWs can ideally provide an enhanced environment to support proliferation and differentiation functions of bone cells. Cell/composite interactions were assessed with suitable assays including viability and alkaline phosphatase activity, while scanning electron microscopy characterization was used to study the morphology of cells grown on composites. Such results suggest that for nanowires in a vertical array, the presence of the polymer improves cellular attachment and overall viability relative to the nanowire-only system.

Silicon nanocrystals (Si-nc) present several plus points as advanced fluorescent biomarkers but suffer from difficulties met in controlling their intrinsic photoluminescence (PL). Here, we first consider the reasons for this difficulty, showing results that support an interface defect-related origin of the PL. Attainment of a controlled PL emission would then require tuning of defects in the capping oxide, a hard and yet unaddressed task. Alternatively, we demonstrate the possible use of Si-nc as antennas, or sensitizers, of a luminescent rare-earth ion in an engineered fluorophore. In this approach the relatively high and broadband optical absorption of Si-nc was exploited, keeping the advantages of a near-infrared inorganic light emitter. Another fundamental part of the assessment of Si-nc for bioimaging is their biocompatibility. Here, we report toxicity tests based on the lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays on epithelial cells and fibroblasts, confirming that Si-nc in concentration suitable for luminescent labeling do not affect significantly the cells viability.

Luminescent nanocrystals or quantum dots (QDs) have great potential for bioanalysis as well as optoelectronics. Here we report an effective and inexpensive fabrication method of silicon carbide quantum dots (SiC QDs), with diameter below 8 nm, based on electroless wet chemical etching. Our samples show strong violet-blue emission in the 410–450 nm region depending on the solvents used and particle size. The cytotoxic properties of the SiC QDs based on alamarBlueTM assay cells were studied. The presence of the QDs dots does not affect cell growth in a wide concentration range. Two-photon excitation showed significant response from SiC nanocrystals that were injected into hippocampal CA1 pyramidal cells.

We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications.

Stable, aqueous, red-to-near infrared emission is critical for the use of silicon nanoparticles (Si NPs) in biological fluorescence assays, but such Si NPs have been difficult to attain. We report a synthesis and surface modification strategy that protects Si NPs and preserves red photoluminescence (PL) in water for more than 6 mo. The Si NPs were synthesized via high temperature reaction, liberated from an oxide matrix, and functionalized via hydrosilylation to yield hydrophobic particles. The hydrophobic Si NPs were phase transferred to water using the surfactant cetyltrimethylammonium bromide (CTAB) with retention of red PL. CTAB apparently serves a double role in providing stable, aqueous, red-emitting Si NPs by (i) forming a hydrophobic barrier between the Si NPs and water and (ii) providing aqueous colloidal stability via the polar head group. We demonstrate preservation of the aqueous red emission of these Si NPs in biological media and examine the effects of pH on emission color.

Porous silicon (PSi) microparticles are designed as tunable delivery carriers for the model anticancer drug, mitoxantrone dihydrochloride (MTX). The surface of the native nanostructured PSi particles was chemically modified by grafting dodecyl and undecanoic acid via thermal hydrosilylation with 1-dodecene and undecylenic acid, respectively. Attenuated total reflectance Fourier transform infrared spectroscopy and nitrogen adsorption–desorption measurements were used to characterize the physiochemical properties of the native and chemically modified PSi microparticles. MTX was loaded by physical adsorption to the native and dodecyl-terminated PSi or by covalent attachment to the undecanoic acid-terminated microparticles. Both drug release profile and the Si erosion of the carriers were significantly affected by the surface chemistry of the PSi microparticles and the drug loading method. The MTX release spans over a period of several hours to weeks, as dictated by these parameters. In vitro cytotoxicity studies on human breast carcinoma (MDA-MB-231) cells revealed that the released MTX maintains its cytotoxic functionality, in comparison to the very low toxicity of all PSi microparticles.

The structural, electronic, and magnetic properties of quasi-one-dimensional MoS2nanowires (NWs), passivated by extra sulfur, have been determined using ab initio density functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images and theoretical literature. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo edge, quasi-one-dimensional metallic states are predominant in all the low-energy model structures despite their reduced dimensionality. These metallic states are localized mainly at the edges. However, the electronic and magnetic character of the NWs does not depend only on the S saturation but also on the symmetry configuration of the S edge atoms. Our results show that for the same S saturation, the magnetization can be decreased by increasing the pairing of the S and Mo edge atoms. In spite of the observed pairing of S dimers at the Mo edge, the NWs do not experience a Peierls-like metal–insulator transition.

In this study, gold (Au) nanowires were synthesized with a modified hydrothermal process, and high structural purity and control over Au nanowire diameter were achieved. Parametric study was performed to examine the effect of surfactant concentration, reaction time, and temperature on the quality of the synthesized products. The optimum conditions were determined for the synthesis with two different surfactant molecules, namely hexamethylenetetramine and ethylenediaminetetraacetic acid. Au nanowires synthesized under optimum conditions have high aspect ratio (diameters in the range of 50–110 nm and lengths in micrometers) with high structural purity and are potentially useful for applications such as surface-enhanced Raman scattering spectroscopy and transparent conducting electrodes for optoelectronic devices.

Precise spatial ordering of quantum dots (QDs) may enable predictable quantum states due to direct exchange interactions of confined carriers. The realization of predictable quantum states may lead to unique functionalities such as spin cluster qubits and spintronic band gap systems. To define exemplary quantum architectures, one must develop control over QD size and spatial arrangement on the sub-35-nm length scale. We use fine-probe electron beam irradiation to locally decompose ambient hydrocarbons onto a bare Si(001) surface. These carbonaceous patterns are annealed in ultrahigh vacuum (UHV), forming ordered arrays of nanoscale SiC QDs. We have achieved sub-10-nm diameter epitaxially oriented 3C-SiC nanodots with interdot spacings down to 22.5 nm. We investigate the templated feature evolution during UHV annealing and subsequent Ge epitaxial overgrowth to identify key mechanisms that must be controlled to preserve pattern fidelity and reduce broadening of the nanodot distribution.