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In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layerblends of poly(3-hexyl thiophene) and [6,6]-phenyl-C 61 -butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly (3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV−vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%). ■ INTRODUCTIONPolymer solar cells (PSCs) are promising technologies of utilizing renewable energy for mass production because of their lightweight and cost-effective production with simple processability. At present, the best power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) PSCs have reached 6− 8% under AM 1.5G conditions. 1−3 After optimizing the thickness and morphology of the donor−acceptor interface of a blended film, consisting of a semiconducting polymer as the donor and a soluble fullerene as the acceptor, a BHJ photoactive layer having a thickness of approximately 200 nm would provide a high fill factor (FF) and an enhanced possibility of exciton dissociation and electrical transportation. 4−6 Furthermore, low-bandgap (LBG) materials can be used to further enhance the device performance by extending the absorption region to longer wavelength. 7−9 Although LBG materials are often associated with lower hole mobilities than are conventional poly(3-hexylthiophene) (P3HT) materials, these charge-transport problems can be overcome by decreasing the thickness of the photoactive layer, albeit with lower external quantum efficiencies (EQEs). Therefore, it is necessary to develop light-concentrating systems to enhance the light trapping efficiency of thinner active layers, especially for use in normal PSC device architectures.Recently, plasmonic light trapping has been applied to effectively enhance the light harvesting performance of solar cells, featuring either continuous metal films [through the excitation of surface plasmon polaritons (SPPs)] or metal nanoparticles [through scattering or localized surface plasmon resonance (LSPR) effects]. 10−18 In PSC devices using SPPs, the electromagnetic wave propagating along the interface between the active layer and back contact electrode should result in higher light trapping efficiency. The short-range EQE enhancement was observed, however, only at a certain excitation wavelength, which was related to the distance and height of the periodic grating structures of th...

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Here, we report the facile preparation of tunable magnetic Ni-doped near-infrared (NIR) quantum dots (MNIR-QDs) as an efficient probe for targeting, imaging, and cellular sorting applications. We synthesized the MNIR-QDs via a hot colloidal synthesis approach to yield monodisperse and tunable QDs. These hydrophobic QDs were structurally and compositionally characterized and further functionalized with amino-PEG and carboxyl-PEG to improve their biocompatibility. Since QDs are known to be toxic due to the presence of cadmium, we have evaluated the in vitro and in vivo toxicity of our surface-functionalized MNIR-QDs. Our results revealed that surface-functionalized MNIR-QDs did not exhibit significant toxicity at the concentrations used in the experiments and are therefore suitable for biological applications. For further in vitro applications, we covalently linked folic acid to the surface of amino-PEG-coated MNIR-QDs through NHS chemistry to target the folate receptors largely present in the HeLa cells to demonstrate the specific targeting and magnetic behavior of these MNIR-QDs. Improved specificity has been observed with treatment of HeLa cells with the folic acid-linked amino PEG-coated MNIR QDs (FA-PEG-MNIR-QDs) compared to the one without folic acid. Since the synthesized probe has magnetic property, we have also successfully demonstrated sorting between the cells which have taken up the probe with the use of a magnet. Our findings strongly suggest that these functionalized MNIR-QDs can be a potential probe for targeting, cellular sorting, and bioimaging applications.

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In the present study, we demonstrate the synthesis and applications of multifunctional gold nanorod-based probes for specific targeting and noninvasive imaging based on localized heating generated by gold nanorods after NIR irradiation. The structural design of the probe consists of MUA (11-mercaptoundecanoic acid)-capped gold nanorods covalently linked with low-molecular-weight chitosan oligosaccharide (M(w) ~5000) via carbodiimide (EDC) coupling agent. This surface modification is performed for complete replacement of toxic CTAB (hexadecyltrimethyl-ammonium chloride) and acid-responsive delivery of gold nanorods in acidic environment as known to be present at tumor surrounding areas. The resulting chitosan oligosaccharide-modified gold nanorods (CO-GNRs) were further conjugated with tumor targeting monoclonal antibody against EGFR (epidermal growth factor receptor) to provide localized targeting functionality owing to the overexpression of EGFR in human oral adenosquamous carcinoma cell line CAL 27. Initial in vitro and in vivo toxicity assessments indicated that CO-GNRs did not induce any significant toxicity and are thus suitable for biological applications. Furthermore, selective targeting and accumulation of CO-GNRs were observed in vitro via two-photon luminescence imaging studies in CAL 27, which was also observed through in vivo targeting studies performed via NIR (near-infrared) laser irradiation in CAL 27 xenografts of BALB/c nude mice. Hence, the CO-GNRs that we have developed are biocompatible and nontoxic and can be a potential candidate for in vivo targeted delivery, noninvasive imaging based on localized hyperthermia, and photothermal-related therapies.

A simple, sensitive, and highly specific lipid targeting Raman probe (Nile red coated silver nanoparticles) has been developed to image living nematode Caenorhabditis elegans (C. elegans). Our idea of imaging lipids in C. elegans is to combine the specificity of the fluorescent dye, Nile red, and the highly enhanced Raman scattering on the silver nanoparticles. Our strategy involves the fabrication of a lipid targeting probe, which is incorporated into the intracellular intestinal granules of C. elegans by incubating these worms in the solution containing Raman probes, resulting in an uptake and subsequent incorporation of these Raman probes into the intestinal granule, thus allowing fast visualization of lipid droplets through a conventional confocal imaging technique.