Comparative analysis of cobalt ferrite and iron oxide nanoparticles using bimodal hyperthermia, along with physical and in silico interaction with human hemoglobin.

Magnetic nanoparticles (MNPs) have captivated the scientific community towards biomedical applications owing to their numerous distinctive physio-chemical properties. In this work, cobalt ferrite (CFNPs) and iron oxide nanoparticles (IONPs) were synthesized using the thermal decomposition method and then functionalized with polyacrylic acid (PAA) for aqueous dispersion. Associated techniques, namely TEM, FESEM, DLS, XRD, and VSM, were used to characterize the synthesized nanoparticles. We also investigated the light-induced and magnetic-field-induced hyperthermia properties of the PAA-functionalized MNPs. It was found that the PAA-CFNPs show a high specific absorption rate (SAR) compared with the PAA-IONPs. Since blood plasma is essential for the delivery and targeting of drugs, studying biological interactions is crucial for effective therapeutic use. Therefore, we performed physical and in silico studies to probe into the mechanistic interaction of CFNPs and IONPs with human hemoglobin. From these studies, we inferred the successful binding between the nanoparticles and protein. Preliminary in vitro cytocompatibility and photothermal toxicity studies in breast cancer (MCF-7) cells treated with the nanoparticles revealed a low dark toxicity and significant laser-induced photothermal toxicity.

Floating metal layer as top electrode over vertically aligned nanorod arrays using angle deposition technique.

A floating metal layer (FML) is realized over vertically aligned nanorod arrays (NRAs) using a newly developed angle deposition technique (ADT) that utilizes simultaneous metallization from two identical metal sources. The angle of the sources formed with the tip of the nanorod creates a shadow onto adjacent nanorods in the deposition direction. Computational estimation suggests the length of nanorods embedded in FML depends on the length of NRAs and separation distance between them, and normal height and lateral distance of sources from surface of the substrate. A layer of copper (Cu) is metalized using the proposed ADT on top of hydrothermally grown titanium dioxide NRAs (TiO2-NRAs) formed over fluorine-doped tin oxide (FTO) coated glass substrate (Cu/TiO2-NRA/FTO). Current-voltage characteristics through the resulting Cu/TiO2-NRA/FTO vertical device structure in macroscopically large area recorded by sweeping DC-voltage in cycles of [Formula: see text] exhibits resistive switching with transition from high to low resistance state during [Formula: see text] and regaining of the original high resistance state following negative differential resistance behavior during [Formula: see text].

Bi-enzyme functionalized electro-chemically reduced transparent graphene oxide platform for triglyceride detection.

Recently, increased attention has been drawn to application of graphene and its derivatives for construction of biosensors, since they can be used to rapidly detect the presence of bio-analytes. Present paper establishes the preparation of a unique transducer which relies on toluidine blue (TB), absorbed by electrochemically reduced graphene oxide (ERGO) transparent thin film onto the surface of the indium tin-oxide (ITO) glass electrode. The proposed TB/ERGO/ITO electrode shows excellent reversible electro-chemical properties. The novel platform has been explored to fabricate a triglyceride (TG) biosensor via co-immobilizing of lipase (LIP) and glycerol dehydrogenase (GDH) onto TB/ERGO/ITO electrode surface. The fabricated bioelectrode (LIP-GDH/TB/ERGO/ITO) directly oxidizes glycerol (produced by catalytic hydrolysis of tributyrin acting as a model TG) in the presence of GDH. The developed bioelectrode replaces unstable biological irreversible redox mediators NAD+/NADH, involved in the triglyceride breakdown reaction. NADH causes fouling on the bioelectrode surface in bi-enzymatic estimation of TG and reduces the shelf-life of biosensor. Electrochemical response studies carried out using cyclic voltammetry reveal that the fabricated electrode can detect tributyrin in the range of 50-400 mg dL-1 with high sensitivity of 29 pA mg-1 dL, low response time of 12 s, long-term stability and a low apparent Michaelis-Menten constant (Kappm) of 0.18 mM, indicating high enzyme affinity of LIP-GDH/TB/ERGO/ITO bioelectrode towards tributyrin. Furthermore, this modified bioelectrode has been explored for estimation of TG with negligible interference in human serum samples. The proposed bi-enzymatic bioelectrode for TG analysis offers an efficient and novel interface for application of graphene and its derivatives in the field of bioelectronic devices.

Tuneable Physicochemical Properties of Thermally Annealed Graphene Oxide Powder and Thin Films.

The tuneability of oxygen containing groups in graphene oxide (GO) that controls physicochemical properties is highly desirable for device applications. In this context, the thermally reduced graphene oxide (r-GO) powders and spin coated thin films with varying sp2/sp3 carbon network have been prepared using highly exfoliated GO (synthesized using modified Hummer's method with an innovative conjunction of lyophilisation). The additional step of lyophilisation results in the formation of highly exfoliated and monodispersed GO nanosheets as evidenced from FESEM, TEM, XRD, and Raman, FT-IR and UV-Vis spectroscopy. Spectroscopic analysis revealed the systematic evolution of r-GO with tuneable structural, optical and electrical properties as results of varying annealing temperatures (100-400 °C), due to restoration of sp2 conducting carbon network i.e., the formation of new -C═C- network and Stones-Wales defect. The tuneability of physical properties is further corroborated by change in the resistance values, as evidenced through the current-voltage characteristics in GO thin film based lateral device structures with Ag and Al top contacts. Controlling physicochemical properties at relatively low processing temperature warrants the utilization of GO and r-GO in various electronic and optoelectronic devices.

Probing the Mechanism for Bipolar Resistive Switching in Annealed Graphene Oxide Thin Films.

The bipolar resistive switching (BRS) between a metallic low resistance state (LRS) and an insulating high resistance state (HRS) is demonstrated for annealed graphene oxide (GO) thin film-based device structures with aluminum (Al) as one of the contact electrodes. An optimal switching of ∼104 order is recorded for Al/GO (200 °C)/indium tin oxide (ITO) among the device structures in metal (M2)/GO (T)/metal (M1) configurations (M1 = Al, Au, or ITO and M2 = Au or Al), fabricated using GO (T)/metal (M1), annealed at different temperatures, T = 100, 200, 300, and 400 °C. The initial Ohmic conduction for electronic transport and the presence of metal contents through GO thin films in the X-ray photoelectron spectroscopy support the physical evidence of Al filament formation between the two electrodes as imaged by the high-resolution transmission electron microscopy. The speculated mechanism for BRS in repeated voltage sweep cycles is attributed to the current triggered breaking of metal filaments because of the combined effect of Joule's heating and Peltier heat generation at LRS → HRS transition, and electric field induced migration of metal atoms, leading to the formation of metal filaments through the GO film at the HRS → LRS transition. The higher switching ratio exhibited in the current study could be translated to engineer simple and low-cost resistive memory devices.

Biosensing Test-Bed Using Electrochemically Deposited Reduced Graphene Oxide.

The development of an efficient test-bed for biosensors requires stable surfaces, capable of interacting with the functional groups present in bioentities. This work demonstrates the formation of highly stable electrochemically reduced graphene oxide (ERGO) thin films reproducibly on indium tin oxide (ITO)-coated glass substrates using a reliable technique through 60 s chronoamperometric reduction of a colloidal suspension maintained at neutral pH containing graphene oxide in deionized water. Structural optimization and biocompatible interactions of the resulting closely packed and uniformly distributed ERGO flakes on ITO surfaces (ERGO/ITO) are characterized using various microscopic and spectroscopic tools. Lipase enzyme is immobilized on the ERGO surface in the presence of ethyl-3-[3-(dimethylamino)propyl]carbodimide and N-hydroxysuccinimide for the detection of triglyceride in a tributyrin (TBN) solution. The ERGO/ITO surfaces prepared using the current technique indicate the noticeable detection of TBN, a source of triglycerides, at a sensitivity of 37 pA mg dL(-1) cm(-2) in the linear range from 50 to 300 mg dL(-1) with a response time of 12 s. The low apparent Michaelies-Menten constant of 0.28 mM suggests high enzyme affinity to TBN. The currently developed fast, simple, highly reproducible, and reliable technique for the formation of an ERGO electrode could be routinely utilized as a test bed for the detection of clinically active bioentities.

Electronic transport through ruthenium-based redox-active molecules in metal-molecule-metal nanogap junctions.

Electronic transport through ruthenium-based redox-active organometallic molecules is measured by self-assembling diruthenium(III) tetra(2-anilinopyridinate)-di(4-thiolphenylethynyl) (trans-Ru2(ap)4(C'CC6H4S-)2 (A) and trans- Ru2(ap)4((C'CC6H4)2S-)2 (B) molecules in nanogap molecular junctions. Voltage sweeps at a high scan rate show low bias current peaks (at +/-0.35 +/- 0.05 V for A and +/-0.27 +/- 0.05 V for B), which change to plateaus in slow bias scans and a second conductance peak at approximately +/-1.05 +/- 0.15 V. The peaks/plateaus are not observed in the return bias sweeps, possibly due to charge storage in the molecules. The energy states for the molecular orbitals of these molecules as estimated from the conductance peaks are in close agreement with the respective energy values from voltammetric measurements in solution.

Electrical readouts of single and few molecule systems in metal-molecule-metal device structures.

Electrical conduction through molecular junctions are measured in different local environments through two test beds that are ideal for single/few molecule and molecular monolayer systems. A technique has been developed to realize Au films with approximately 1.5 A surface roughness comparable to the best available techniques and suitable for formation of patterned device structures. The technique utilizes room temperature e-beam evaporated Au films over oxidized Si substrates silanized with (3-mercaptopropyl)trimethoxysilane (MPTMS). The lateral (single/few molecule) and vertical (many molecules) device structures are both enabled by the process for realizing ultraflat Au layer. Lateral metal-molecule-metal (M-M-M) device structures are fabricated by forming pairs of Au electrodes with nanometer separation (nano-gap) through an electromigration-induced break-junction (EIBJ) technique at room temperature and conductivity measurements are carried out for dithiol functionalized single molecules. We have used the flat Au layer (using the current technique) as the bottom contact in vertical M-M-M device structures. Here, molecular self-assembly are formed on the Au surface, and patterned (20 x 20 microm2) top Au contacts were successfully transferred on to the device using a stamping technique (where the Au is deposited on a polydimethylsiloxane (PDMS) pad and following a physical contact on the thiolated Au layer). The single molecular property of XYL, a highly conductive molecule and many molecular property of HS-C9-SH, an insulating molecule in its molecular monolayer form are measured. Observation of enhanced conduction following molecular deposition, and comparison of conductance-voltage characteristics to those predicted theoretically, confirms the success of trapping single/few molecules in the nano-gap. The observed approximately 10(2) less conductance through the molecular monolayer of HS-C9-SH compared to the estimation of a linear sum of single molecule conductances over large area indicate that either all the molecules are not in physical contact with the top stamping electrode or electrode-molecule coupling has a less broadening in presence of it own environment or both.