Hybrid nanomaterials having tunable properties that can be reversibly conducted by external stimuli, in a particular light, are of great importance since they enable synergetic behavior between their components and enable the design of stimuli responsive “smart” materials and surfaces. Here we describe the formation of organic–inorganic hybrid nanoparticles that photochemically aggregate and their effect on the electronic properties of a semiconducting surface, as a function of external irradiation. The inorganic component consists of 3 nm gold nanoparticles while the organic component is a covalently attached, photochromic spiropyran derivative. Aggregation/deaggregation patterns in solution were obtained and analyzed by UV–vis spectroscopy and transmission electron microscopy upon photoswitching. The assembly of spiropyran-modified gold nanoparticles on an Si/SiO2 surface proved useful in phototuning the electronic properties of semiconductors measured by contact potential difference.
Zinc and copper are essential metal ions for numerous biological processes. Their levels are tightly maintained in all body organs. Impairment of the Zn2+ to Cu2+ ratio in serum was found to correlate with many disease states, including immunological and inflammatory disorders. Oxytocin (OT) is a neuropeptide, and its activity is modulated by zinc and copper ion binding. Harnessing the intrinsic properties of OT is one of the attractive ways to develop valuable metal ion sensors. Here, we report for the first time an OT-based metal ion sensor prepared by immobilizing the neuropeptide onto a glassy carbon electrode. The developed impedimetric biosensor was ultrasensitive to Zn2+ and Cu2+ ions at physiological pH and not to other biologically relevant ions. Interestingly, the electrochemical impedance signal of two hemicircle systems was recorded after the attachment of OT to the surface. These two semicircles suggest two capacitive regions that result from two different domains in the OT monolayer. Moreover, the change in the charge-transfer resistance of either Zn2+ or Cu2+ was not similar in response to binding. This suggests that the metal-dependent conformational changes of OT can be translated to distinct impedimetric data. Selective masking of Zn2+ and Cu2+ was used to allow for the simultaneous determination of zinc to copper ions ratio by the OT sensor. The OT sensor was able to distinguish between healthy control and multiple sclerosis patients diluted sera samples by determining the Zn/Cu ratio similar to the state-of-the-art techniques. The OT sensor presented herein is likely to have numerous applications in biomedical research and pave the way to other types of neuropeptide-derived sensors.
In this work, we demonstrate the tunability of electronic properties of Si/SiO2 substrates by molecular and ionic surface modifications. The changes in the electronic properties such as the work function (WF) and electron affinity were experimentally measured by the contact potential difference technique and theoretically supported by density functional theory calculations. We attribute these molecular electronic effects mainly to the variations of molecular and surface dipoles of the ionic and neutral species. We have previously shown that for the alkylhalide monolayers, changing the tail group from Cl to I decreased the WF of the substrate. Here, we report on the opposite trend of WF changes, that is, the increase of the WF, obtained by using the anions of these halides from Cl– to I–. This trend was observed on self-assembled alkylammonium halide (−NH3+ X–, where X– = Cl–, Br–, or I–) monolayer-modified substrates. The monolayer’s formation was supported by ellipsometry measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. Comparison of the theoretical and experimental data suggests that the ionic surface dipole depends mainly on the polarizability and the position of the counter halide anion along with the organization and packaging of the layer. The described ionic modification can be easily used for facile tailoring and design of the electronic properties Si/SiO2 substrates for various device applications.
Copper ions play a major role in biological processes. Abnormal Cu2+ions concentrations are associated with various diseases, hence, can be used as diagnostic target. Monitoring copper ion is currently performed by non-portable, expensive and complicated to use equipment. We present a label free and a highly sensitive electrochemical ion-detecting biosensor based on a Gly-Gly-His tripeptide layer that chelate with Cu2+ ions. The proposed sensing mechanism is that the chelation results in conformational changes in the peptide that forms a denser insulating layer that prevents RedOx species transfer to the surface. This chelation event was monitored using various electrochemical methods and surface chemistry analysis and supported by theoretical calculations. We propose a highly sensitive ion-detection biosensor that can detect Cu2+ ions in the pM range with high SNR parameter.
Carbon nanotubes (CNTs) and semiconductor nanocrystals (SCNCs) are known to be interesting donor–acceptor partners due to their unique optical and electronic properties. These exciting features have led to the development of novel composites based on these two nanomaterials and to their characterization for use in various applications, such as components in sensors, transistors, solar cells and biomedical devices. Two approaches based on covalent and noncovalent methods have been suggested for coupling the SCNCs to CNTs. Most covalent conjugation methods used so far were found to disrupt the electronic structure of the CNTs or interfere with charge transfer in the CNT–SCNC interface. Moreover, it offers random and poorly organized nanoparticle coatings. Therefore, noncovalent methods are considered to be ideal for better electronic coupling. However, a key common drawback of noncovalent methods is the lack of stability which hampers their applicability. In this article, a method has been developed to couple semiconductor seeded nanorods onto CNTs through π–π interactions. The CNTs and pyrene conjugated SCNC hybrid materials were characterized by both microscopic and spectroscopic techniques. Fluorescence and photocurrent measurements suggest the proposed pi-stacking approach results in a strong electronic coupling between the CNTs and the SCNCs leading to better photocurrent efficiency than that of a covalent conjugation method reported using similar SCNC material. Overall, the CNT–SCNC films reported in the present study open the scope for the fabrication of optoelectronic devices for various applications.
Polycrystalline SnO2 1D nanostructures with diameters of 150–200 nm and consisting of uniformly sized single-crystallites of ~ 10 nm in size were produced via aqueous sol-gel and hard template assisted methods. Stable sols were prepared from tin oxalate precursor, citric acid and H2O2. Solution chemistry and parameters influencing the stability of the sol and morphological structure of the resulting materials are addressed. Morphological and structural characterization revealed uniform and porous structure of the nanostructured SnO2. Hollow nanotubular structures were produced from solutions of lower concentration. Results of XPS analysis revealed that a sub-stoichiometric phase with surface composition of SnO1.8 was obtained indicating the formation of oxygen vacancies. The optical properties were investigated and optical band gap energy for the powder samples was estimated to be 3.61 eV. An environmentally friendly aqueous sol-gel route developed to prepare homogeneous nanostructures of 1D SnO2 will enable facile fabrication of various oxide based nanostructured materials.