Dip-Pen Nanolithography (DPN) uses an AFM tip to deposit organic molecules through a meniscus onto an underlying substrate under ambient conditions. Thus far, the methodology has been developed exclusively for gold using alkyl or aryl thiols as inks. This study describes the first application of DPN to write organic patterns with sub-100 nm dimensions directly onto two different semiconductor surfaces: silicon and gallium arsenide. Using hexamethyldisilazane (HMDS) as the ink in the DPN procedure, we were able to utilize lateral force microscopy (LFM) images to differentiate between oxidized semiconductor surfaces and patterned areas with deposited monolayers of HMDS. The choice of the silazane ink is a critical component of the process since adsorbates such as trichlorosilanes are incompatible with the water meniscus and polymerize during ink deposition. This work provides insight into additional factors, such as temperature and adsorbate reactivity, that control the rate of the DPN process and paves the way for researchers to interface organic and biological structures generated via DPN with electronically important semiconductor substrates.

Rapid and accurate molecular blood analysis is essential for disease diagnosis and management. Field Effect Transistor (FET) biosensors are a type of device that promise to advance blood point-of-care testing by offering desirable characteristics such as portability, high sensitivity, brief detection time, low manufacturing cost, multiplexing, and label-free detection. By controlling device parameters, desired FET biosensor performance is obtained. This review focuses on the effects of sensing environment, micro/nanoscale device structure, operation mode, and surface functionalization on device performance and long-term stability.

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Synthetic TAT peptides designed to contain an arginine rich basic unit can bind to RNA with an affinity and specificity of a full-length TAT protein. Therefore, deducing strategies to immobilize such short peptides to surfaces can enable one to study their unique recognition properties in various types of sensor platforms. In this paper, we present a strategy to immobilize a 15-residue TAT peptide (CGISYGRKKRRQRRR) in the form of nanoscopic features on SiO x surfaces. The protocol is based on dip-pen nanolithography that results in the formation of a covalent attachment of the peptide to a SiO x surface rather than immobilization via electrostatic interactions or patterning on metal surfaces. The nanolithography was characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy. Critical parameters identified by this report include roughness quality and chemical composition of the surface prior to patterning, high humidity conditions, and concentration of ink solution needed to modify the AFM tip. Furthermore, the nanoscopic features were successfully used in recognition experiments where an RNA sequence with a loop structure, known for its specific interaction with the peptide, was tested. The results in this report indicate that one can use nanolithographic strategies to pattern chemically modified “soft” SiO x surfaces and therefore provide a proof-of-concept experiment that can be transferred in complex microfabricated semiconductor architectures. Developing such patterning methodologies, along with the reported surface characterization protocol, is essential for precise and selective multicomponent placement of biologically active molecules on microcantilever based devices or other types of bio-MEMS platforms.

The study describes how DNA coated with magnetic nanoparticles remains biologically active and accessible to the BamH1 restriction enzyme. Long DNA molecules are coated with magnetic nanoparticles using electrostatic interactions. The coated, stretched, and surface-bound DNA is incubated in the restriction enzyme that specifically recognizes any strand containing the GGATCC base sequence and clips the DNA. We show that, despite the presence of the nanoparticles on the DNA, the enzyme is still able to recognize the cleavage site and effectively digest the assembly.

In this study, a mesoporous silica nanoparticle (MSN)-based nerve growth factor (NGF) delivery system has been successfully embedded within an electroactive polypyrrol (Ppy). The spherical particles with approximately 100 nm diameter possess a large surface-to-volume ratio for the entrapment of NGF into the pores of MSNs while retaining their bioactivity. Direct incorporation of MSN-NGF within Ppy was achieved during electrochemical polymerization. The loading amount and release profile of NGF from the composite was investigated by sandwich ELISA. The NGF incorporation can be controllable by varying particle concentration or by extending electrodeposition time. The morphology and chemical composition of the Ppy/MSN-NGF composite was evaluated by atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). Optical and electron microscopy revealed a characteristic attachment of PC 12 cells and the outgrowth of their neurites when grown on the Ppy/MSN-NGF composite as a result of a sustained and controlled release of NGF. In order to observe the effectiveness of electrical stimulation, neurite extension of cells cultured on unstimulated and stimulated Ppy/MSN-NGF was compared. The NGF release in the presence of electrical stimulation promoted significantly greater neurite extension.

The structure and magnetic properties of different types of templated wires are compared in this study. A long DNA molecule was used to guide the assembly of pyrrolidinone-capped Fe2O3 and CoFe2O3 particles as well as polylysine-coated gold nanoparticles. The resulting DNA-templated wires were stretched onto silicon oxide surfaces using a receding meniscus procedure. The coated, stretched, and surface-bound wires were characterized using atomic force microscopy (AFM), magnetic force microscopy (MFM), and spectroscopic methods. The results with respect to the wire properties were correlated with those determined from the bulk properties of the nanoparticles and with the properties of the bulk DNA. The MFM measurements allowed us to visualize the formation of domains along the wires as well as qualitatively compare the magnetic properties of each templated structure.

Four TAT peptide fragments were used to functionalize GaAs surfaces by adsorption from solution. In addition, two well-studied alkylthiols, mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) were utilized as references to understand the structure of the TAT peptide monolayer on GaAs. The different sequences of TAT peptides were employed in recognition experiments where a synthetic RNA sequence was tested to verify the specific interaction with the TAT peptide. The modified GaAs surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). AFM studies were used to compare the surface roughness before and after functionalization. XPS allowed us to characterize the chemical composition of the GaAs surface and conclude that the monolayers composed of different sequences of peptides have similar surface chemistries. Finally, FT-IRRAS experiments enabled us to deduce that the TAT peptide monolayers have a fairly ordered and densely packed alkyl chain structure. The recognition experiments showed preferred interaction of the RNA sequence toward peptides with high arginine content.