Plasmonic polyaniline/gold nanorods hybrid composites for selective NIR photodetection: Synthesis and characterization

Abstract In this study, we present the development of polyaniline/gold nanorod nanocomposites and the effect of the nanorods' aspect ratio and concentration on the overall electrical conductivity of nanocomposite systems. The electrical characterization showed that at the same atomic gold concentration, the conductivity of the nanocomposites increased by about 14% after increasing the gold nanorods' aspect ratio from 2.9 to 3.8. Furthermore, the conductivity of the nanocomposites increases linearly with the concentration of atomic gold, keeping the nanorods' aspect ratio stable, due to increasing the metallic content. The interaction between polyaniline and gold nanorods was investigated by FTIR, micro Raman, and XPS spectroscopic techniques, indicating the delocalization of the charges across the polymer chains induced by the incorporation of the nanorods. The interaction most likely occurs through the imine nitrogen of the polymer's backbone. The homogenous distribution of the gold nanorods in the polyaniline matrix was verified by TEM. Furthermore, the selective photosensitivity of the developed nanocomposites to NIR light was examined, and an increase in their current density was detected when the nanocomposites were irradiated at the wavelength that coincides with the longitudinal plasmonic resonance absorption of the incorporated nanorods. We foresee applications of the developed nanocomposites in numerous optoelectronic sectors

Photochemical synthesis: Effect of UV irradiation on gold nanorods morphology

Abstract Gold nanorods (AuNRs) were synthesized by photochemical method, through irradiation of a reaction solution, containing gold precursor, surfactant and a mild reducing agent to speed up the process. The effects of the irradiation parameters on the morphology of the formed AuNRs were investigated by UV–Vis absorption spectra and transmission electron microscopy. Specifically, the control of the UV irradiance (irradiation power per unit area) and irradiation time allowed the preparation of AuNRs with a wide range of sizes. Increase of the irradiation power leads to the formation of smaller AuNRs, with concomitant decrease of length and diameter. Since both axes show a simultaneous size decrease, the produced AuNRs have increased aspect ratio. Overall we show that application of high UV irradiance for short times favors the synthesis of small AuNRs with increased anisotropy. We propose that the rise of the irradiation power primarily accelerates the reduction of the gold precursor, promoting in such way the formation of smaller seeds. Short irradiation times guard against dissolution effects on the formed nanorods

Effect of precursor solution dark incubation on gold nanorods morphology

Abstract Gold nanorods were synthesized in an aqueous solution of hexadecyltrimethylammonium bromide via a combination of chemical reduction and UV photoirradiation. Gold ligand complexes, present in the stock solution, are initially reduced, by ascorbic acid as mild reducing agent. The gold ions nucleation and colloid growth proceeds then by subsequent UV irradiation of the so-obtained precursor solution. We present a systematic study of the effect of incubation of the precursor solution on the dispersion state and aspect ratio of the produced nanorods. Incubation of the precursor solution allows the synthesis of higher aspect ratio nanorods with narrower size distribution compared to those obtained without incubation. We propose a mechanism for the gold nanorods formation including two stages, a nucleation and a diffusive growth. This allows us to explain the synthesis improvement as a consequence of the increase in the size of the gold ligand complexes aggregates, leading to a decrease of the nanorods growth rate

Using Impedance Measurements to Characterize Surface Modified with Gold Nanoparticles

With the increased practice of preventative healthcare to help reduce costs worldwide, sensor technology improvement is vital to patient care. Point-of-care (POC) diagnostics can reduce time and lower labor in testing, and can effectively avoid transporting costs because of portable designs. Label-free detection allows for greater versatility in the detection of biological molecules. Here, we describe the use of an impedance-based POC biosensor that can detect changes in the surface modification of a micro-fabricated chip using impedance spectroscopy. Gold nanoparticles (GNPs) have been employed to evaluate the sensing ability of our new chip using impedance measurements. Furthermore, we used impedance measurements to monitor surface functionalization progress on the sensor’s interdigitated electrodes (IDEs). Electrodes made from aluminum and gold were employed and the results were analyzed to compare the impact of electrode material. GNPs coated with mercaptoundecanoic acid were also used as a model of biomolecules to greatly enhance chemical affinity to the silicon substrate. The portable sensor can be used as an alternative technology to ELISA (enzyme-linked immunosorbent assays) and polymerase chain reaction (PCR)-based techniques. This system has advantages over PCR and ELISA both in the amount of time required for testing and the ease of use of our sensor. With other techniques, larger, expensive equipment must be utilized in a lab environment, and procedures have to be carried out by trained professionals. The simplicity of our sensor system can lead to an automated and portable sensing system

Effect of Anderson localization on light emission from gold nanoparticle aggregates

The localization of light known as Anderson localization is a common phenomenon characterizing aggregates of metallic nanostructures. The electromagnetic energy of visible light can be localized inside nanostructures below the diffraction limit by converting the optical modes into nonradiative surface plasmon resonances. The energy of the confined photons is correlated to the size and shape of the nanostructured system. In this work, we studied the photoluminescence dependence of aggregates of 14 nm diameter gold nanoparticles (AuNPs) synthesized by drop-casting a liquid suspension on two different substrates of glass and quartz. The AuNP aggregates were characterized by electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The dielectric constant of the surrounding medium plays a crucial role in determining the aggregate geometry, which affects the Anderson localization of light in the aggregates and hence causes a red-shift in the plasmonic resonance and in the photoluminescence emission. The geometry of the gold nanoparticle aggregates determine the strength of the Anderson localization, and hence, the light emission from the aggregates. The photoluminescence lifetime was found to be dependent on the AuNP aggregate geometry and the dielectric constant of the medium

Label-free impedimetric immunosensor for point-of-care detection of COVID-19 antibodies

Abstract The COVID-19 pandemic has posed enormous challenges for existing diagnostic tools to detect and monitor pathogens. Therefore, there is a need to develop point-of-care (POC) devices to perform fast, accurate, and accessible diagnostic methods to detect infections and monitor immune responses. Devices most amenable to miniaturization and suitable for POC applications are biosensors based on electrochemical detection. We have developed an impedimetric immunosensor based on an interdigitated microelectrode array (IMA) to detect and monitor SARS-CoV-2 antibodies in human serum. Conjugation chemistry was applied to functionalize and covalently immobilize the spike protein (S-protein) of SARS-CoV-2 on the surface of the IMA to serve as the recognition layer and specifically bind anti-spike antibodies. Antibodies bound to the S-proteins in the recognition layer result in an increase in capacitance and a consequent change in the impedance of the system. The impedimetric immunosensor is label-free and uses non-Faradaic impedance with low nonperturbing AC voltage for detection. The sensitivity of a capacitive immunosensor can be enhanced by simply tuning the ionic strength of the sample solution. The device exhibits an LOD of 0.4 BAU/ml, as determined from the standard curve using WHO IS for anti-SARS-CoV-2 immunoglobulins; this LOD is similar to the corresponding LODs reported for all validated and established commercial assays, which range from 0.41 to 4.81 BAU/ml. The proof-of-concept biosensor has been demonstrated to detect anti-spike antibodies in sera from patients infected with COVID-19 within 1 h. Photolithographically microfabricated interdigitated microelectrode array sensor chips & label-free impedimetric detection of COVID-19 antibody

Gold nanoparticle-filled biodegradable photopolymer scaffolds induced muscle remodeling: in vitro and in vivo findings

Therapeutic stem cell transplantation bears the promise of new directions in organ and tissue replacement, but a number of its difficulties and perils are also well known. Our goal was to develop a method of transplantation by which the transplanted cells remain confined to the transplantation site and induce favorable processes. With the help of mask-projection excimer laser stereolithography, 3D hybrid nanoscaffolds were fabricated from biodegradable, photocurable PPF:DEF resin with incorporated gold nanoparticles (Au NPs). The scaffolds were tested in vitro and in vivo in order to find out about their biocompatibility and fitness for our purposes. In vitro, macrophages and mouse autologous adipose stem cells (ASCs) were seeded over the hybrid scaffolds and non-hybrid (with Au NPs) scaffolds for 4 days. The hybrid nanocomposite greater stem cell dispension and stem cell adhesion than PPF scaffolds without Au NPs, but such a difference was not seen in the case of macrophages. In vivo, stem cells, scaffoldings and scaffoldings covered in stem cells were transplanted under the back skin of mice. After 14 days, blood samples were taken and the affected skin area was excised. Cytokine and chemokine profiling did not indicate elevated immunomediators in the sera of experimental animals. Interestingly, the autologous-stem-cell-seeded hybrid nanocomposite scaffold induced muscle tissue regeneration after experimental wound generation in vivo. We could not observe such stem cell-induced tissue regeneration when no scaffolding was used. We conclude that PPF:DEF resin nanoscaffolds with incorporated gold nanoparticles offer a safe and efficient alternative for the enhancement of local tissue remodeling. The results also support the idea that adipose derived stem cells are an optimal cell type for the purposes of regenerative musculoskeletal tissue engineering. © 201