We fabricate SERS sensors by inkjet printing and demonstrate that their SERS response correlates with their diffuse reflectance characteristics. Using a modified commercial inkjet-printer, SERS sensors are prepared with multiple printing passes. Performances of the printed sensors only become noticeable after five printing passes as observed in both SERS and diffuse reflectance measurements. This suggests that the simpler diffuse reflectance measurement can be used as an alternative method to characterize and optimize the SERS performance of the printed sensors. Although sensors with a very high number of printing passes exhibit a much stronger SERS response from the benzenethiol reporter molecule, we also noticed a significant increase in the background from blank sensors. This may not be a desirable feature particularly for the detection of weakly bound molecules. Controlling SERS background and attaining a desirable SERS enhancement would need to be balanced in the design of sensors for the end-user’s specific need.
Inkjet-printed surface enhanced Raman spectroscopy (SERS) sensors are fabricated on cellulose based paper or fabric substrates. These flexible sensors provides basic point-of-sampling advantages that is particularly useful in field applications. Due to the heterogeneous loading of nanoparticles on the substrate, SERS intensities inevitably vary across the active area of the printed sensor. This paper will discuss the use of receiver operating characteristics (ROC) for the analysis of inkjet-printed SERS sensors. The aim is to provide an alternative measurand to the SERS enhancement factor that can be used to compare different types of SERS substrates. We have developed statistical analysis from multiple data sets obtained from sensors exposed to both analyte and control to determine the probability of positive detection (PD) at various analyte concentration. This dependence describes the ROC of the sensor and also provides confidence level associated with a given detection limit. We propose this methodology for the evaluation of SERS sensors to enable their field applications.
In this study, we will present the synthesis of self-assembled coupled Au nanorods (NRs) as substrates capable of supporting a dual modality of surface enhanced spectroscopies, SERS and SEIRAS. The AuNR arrays can be assembled either through vertical alignment or lateral alignment. We will present different assembly strategies for the Au NRs by adjusting the ionic strength of the Au NR solution. The goal is to rely on self-assembly to create organized and reproducible sensors for small molecule detection. Field enhancement criteria differs between SERS and SEIRAS. We will also present the finite-difference time-domain (FDTD) simulation of the multilayered AuNR array across visible and SWIR spectral region to explain some of the experimental observations.
The plasmon resonance of noble metal nanoparticles (NP) manifests itself in a variety of extraordinary optical properties.
Resonant excitation of the conduction electrons by incident radiation generates a localized surface plasmon resonance
(LSPR) that is responsible for a variety of surface enhanced optical phenomena. This unique optical property coupled
with well-established surface chemistry allows us to utilize both Ag and Au NP as optical contrasting agents to probe
and monitor the surface receptors of cells. We have employed two plasmon-assisted optical techniques (namely, surface
enhanced Raman scattering, and resonant Rayleigh scattering) to monitor the adrenergic receptors in mammalian
cardiomyocyte cells that have been labeled with functionalized Ag NPs. In this study, a unique Raman reporter
molecule, 4-(mercaptomethyl)benzonitrile, was developed to provide an easily identifiable vibration, the C≡N stretch, in
a spectral window free from Raman bands of cell constituents and other biomolecules used in receptor crosslinking and
surface passivation. Successfully labeled cells were then monitored with both optical techniques. Both techniques are
related through the plasmonic properties of the noble metal NP and combined with high resolution imaging techniques;
we outline the importance that different NP architectures play in the different imaging techniques. Furthermore, we will
discuss the instrumentation and plasmonic implications in the design of NP best suited for such multimodal imaging
approaches.
Multi-modal sensing scheme significantly improves the detection accuracy but can also introduce
extra complexity in the overall design of the sensor. We overcome this difficulty by utilizing the
plasmonic properties of metallic nanoparticles. In this study, we will present a simple dual optical
sensing mechanism which harvests signals of the resonantly excited metallic nanostructure in the
form of surface enhanced Raman scattering (SERS) and resonant Rayleigh scattering. Silver and
gold nanoparticles labeled with appropriate antibodies act as signal transduction units and upon
exposure to the targeted pathogen render the targeted species optically active. We demonstrate that
detection of a single pathogen cell is easily attainable with the dual detection scheme. Furthermore,
we explore the markedly different SERS intensity observed from the use of two very different
antibody recognition units during the pathogen labeling process.
Semiconductor devices that are not generally thought of as light sources do emit radiation in the visible and the near infrared as they operate. Observation of this electroluminescence furnishes insight into the operation of the devices and of the circuitry that they constitute but it requires an extremely sensitive light detector and picosecond time resolution. This can be achieved using a Mepsicron photodetector system that enables single photon counting time-correlated imaging with a spatial resolution of about 1 µm and a time resolution approaching 10 ps. Information extracted from the time-resolved imagery can be compared with circuit layout and topology and individual device structures and with electrical measurements that are performed concurrently. These time-correlated measurements allow signal waveforms to be determined optically, much as the waveforms measured electronically with an oscilloscope and microprobing, but with the advantage that the acquisition is entirely non-invasive. Images can be dissected in both space and time to provide information for individual components of a circuit or regions of a device. This imaging equipment has been used in our laboratory for measurements on Si, GaAsP and GaN technologies and analyses will be presented.
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