Insight into factors affecting the presence, degree, and temporal stability of fluorescence intensification on ZnO nanorod ends

Abstract

We have carried out a combined experimental and simulation study identifying the key physical and optical parameters affecting the presence and degree of fluorescence intensification measured on zinc oxide nanorod (ZnO NR) ends. Previously, we reported on the highly localized, intensified, and prolonged fluorescence signal measured on the NR ends, termed as fluorescence intensification on NR ends (FINE). As a step towards understanding the mechanism of FINE, the present study aims to provide an insight into the unique optical phenomenon of FINE through experimental and simulation approaches and to elucidate the key factors affecting the occurrence, degree, and temporal stability of FINE. Specifically, we examined the effect of the length, width, and growth orientation of single ZnO NRs on the NR-enhanced biomolecular emission profile after decorating the NR surfaces with different amounts and types of fluorophore-coupled protein molecules. We quantitatively and qualitatively profiled the biomolecular fluorescence signal from individual ZnO NRs as a function of both position along the NR long axis and time. Regardless of the physical dimensions and growth orientations of the NRs, we confirmed the presence of FINE from all ZnO NRs tested by using a range of protein concentrations. We also showed that the manifestation of FINE is not dependent on the spectroscopic signatures of the fluorophores employed. We further observed that the degree of FINE is dependent on the length of the NR with longer NRs showing increased levels of FINE. We also demonstrated that vertically oriented NRs exhibit much stronger fluorescence intensity at the NR ends and a higher level of FINE than the laterally oriented NRs. Additionally, we employed finite-difference time-domain (FDTD) methods to understand the experimental outcomes and to promote our understanding of the mechanism of FINE. Particularly, we utilized the electrodynamic simulations to examine both near-field and far-field emission characteristics when considering various scenarios of fluorophore locations, polarizations, spectroscopic characteristics, and NR dimensions. Our efforts may provide a deeper insight into the unique optical phenomenon of FINE and further be beneficial to highly miniaturized biodetection favoring the use of single ZnO NRs in low-volume and high-throughput protein assays.

Polarization-resolved mechanistic investigation of fluorescence signal intensification on zinc oxide nanorod ends

“…10–15 Anisotropically shaped materials can possess unique light-matter interaction phenomena different from those seen in their isotropic counterparts. 16,17 Previous studies have shown that light interacting with anisotropic materials can result in optically distinctive responses depending on the polarization state of the light, angle of the incident light, and geometric orientation of the nanomaterial.…”

Evaluation of polarization rotation in the scattering responses from individual semiconducting oxide nanorods

“…Pure and chemically doped NRs with comparable physical dimensions are systematically characterized for their material-dependent elastic scattering responses upon interactions with visible light. Specifically, we have chosen single NRs of ZnO as well as indium tin oxide (ITO) and zinc tin oxide (ZTO) due to their well-known functional benefits as lasers, 20,21 light emitters, 22–25 waveguides, 26–30 photovoltaics, 31 and biosensors 32,33 . We subsequently elucidate an intriguing scattering response of rotation in the polarization direction of the scattered light from individual NRs.…”

Scattering attributes of one-dimensional semiconducting oxide nanomaterials individually probed for varying light-matter interaction angles

“…The insight gained from this study can advance our fundamental understanding of the optical behaviors of the technologically useful nanomaterials and, at the same time, promote the development of highly miniaturized, photonic and bio-optical devices utilizing the spatially controllable, optical responses of the individual semiconducting oxide NRs. [16][17][18][19][20][21][22][23][24] In many of these technologically important applications, the fundamental optical properties of 1D SO nanomaterials govern their functional outcomes. Light can produce various optical and optoelectronic responses from the materials and, therefore, light-matter interactions can be engineered to produce desirable optical properties such as spontaneous and stimulated emission, 1,25-29 waveguiding, 1-3 and evanescence field enhancement.…”

“…One-dimensional (1D) nanomaterials based on semiconducting oxides (SOs) have demonstrated their useful properties in numerous applications of photonics, 1-4 electronics, [5][6][7][8] optoelectronics, 9,10 photovoltaics, [11][12][13][14][15] and chemical/biological sensing. [16][17][18][19][20][21][22][23][24] In many of these technologically important applications, the fundamental optical properties of 1D SO nanomaterials govern their functional outcomes. Light can produce various optical and optoelectronic responses from the materials and, therefore, light-matter interactions can be engineered to produce desirable optical properties such as spontaneous and stimulated emission, 1,25-29 waveguiding, 1-3 and evanescence field enhancement.…”

“…4,[30][31][32] Such examples can be seen in the research efforts previously reported for the development of SO nanomaterials for applications in nanoscale lasers, 25,26,29 subwavelength waveguides, 1-3,33,34 and biodetection platforms. 17,18,20,23,24,33,35 Specifically, nanomaterials of zinc oxide (ZnO), tin oxide (SnO 2 ), indium tin oxide (ITO), and zinc tin oxide (ZTO) have been widely utilized as signal transduction elements in optical detection devices. 5,8,36,37 These past applications have primarily exploited the optical properties of bulk materials or ensembles of nanomaterials.…”