28 research outputs found
First order Rayleigh scatter as a separate component in the decomposition of fluorescence landscapes
Calibration of Surface Plasmon Resonance Refractometers Using Locally Weighted Parametric Regression
Development and Investigation of a Dual-Pad In-Channel Referencing Surface Plasmon Resonance Sensor
Herein, we describe the construction of a novel dual-pad
referencing surface plasmon resonance (SPR) sensor utilizing electrolytic
grafting of diazonium salts to individually functionalize two gold
pads positioned in a single fluidic channel. Using a dove prism, a
simple single axis optical train may be employed without compromising
the analytical performance. Once functionalized, one pad is used as
the analytical sensing pad for detection of molecular interactions
while the other serves as the reference pad, compensating for background
refractive index fluctuations. The reference pad effectively compensates
bulk refractive index changes and temperature variations as well as
other nonspecific effects. The sensor was applied to calibration of
a pH-responsive polymer layer in the presence of bulk refractive index
and temperature variations. Monitoring selective attachment of a protein
is also demonstrated. To our knowledge, this is the first implementation
of in-channel referencing SPR sensor utilizing diazonium salt-based
surface chemistry
Adsorbate鈥揗etal Bond Effect on Empirical Determination of Surface Plasmon Penetration Depth
The penetration depth of surface
plasmons is commonly determined
empirically from the observed response for adsorbate loading on gold
surface plasmon resonance (SPR) substrates. However, changes in the
SPR spectrum may originate from both changes in the effective refractive
index near the metal surface and changes in the metal permittivity
following covalent binding of the adsorbate layer. Herein, the significance
of incorporating an additional adsorbate鈥搈etal bonding effect
in the calculation is demonstrated in theory and in practice. The
bonding effect is determined from the nonzero intercept of a SPR shift
versus adsorbate thickness calibration and incorporated into the calculation
of penetration depth at various excitation wavelengths. Determinations
of plasmon penetration depth with and without the bonding response
for alkanethiolate鈥揼old are compared and are shown to be significantly
different for a thiol monolayer adsorbate system. Additionally, plasmon
penetration depth evaluated with bonding effect compensation shows
greater consistency over different adsorbate thicknesses and better
agreement with theory derived from Maxwell鈥檚 equation, particularly
for adsorbate thicknesses that are much smaller (<5%) than the
plasmon penetration depth. The method is also extended to a more practically
applicable polyelectrolyte multilayer adsorbate system
Sensing with Prism-Based Near-Infrared Surface Plasmon Resonance Spectroscopy on Nanohole Array Platforms
Nanohole
arrays exhibit unique surface plasmon resonance (SPR)
characteristics according to hole periodicity, diameter, and excitation
wavelength (位<sub>SPR</sub>). This contribution investigates
the SPR characteristics and surface sensitivity of various nanohole
arrays with the aim of tuning the parameters for optimal sensing capability.
Both the Bragg surface plasmons (SPs) arising from diffraction by
the periodic holes and the traditional propagating SPs are characterized
with emphasis on sensing capability of the propagating SPs. Several
trends in bulk sensitivity and penetration depth were established,
and the surface sensitivity was calculated from bulk sensitivity and
penetration depth of the SPs for different analyte thicknesses. Increased
accuracy and precision in penetration depth values were achieved by
incorporating adsorbate effects on substrate permittivity. The optimal
nanohole array conditions for highest surface sensitivity were determined
(820 nm periodicity, 0.27 diameter/periodicity, and 位<sub>SPR</sub> = 1550 nm), which demonstrated an increase in surface sensitivity
for the 10 nm analyte over continuous gold films at their optimal
位<sub>SPR</sub> (1300 nm) and conventional visible 位<sub>SPR</sub> (700 nm)
Electrografted Diazonium Salt Layers for Antifouling on the Surface of Surface Plasmon Resonance Biosensors
Electrografted
diazonium salt layers on the surface of surface
plasmon resonance (SPR) sensors present potential for a significant
improvement in antifouling coatings. A pulsed potential deposition
profile was used in order to circumvent mass-transport limitations
for layer deposition rate. The influence of number of pulses with
respect to antifouling efficacy was evaluated by nonspecific adsorption
surface coverage of crude bovine serum proteins. Instead of using
empirical and rough estimated values, the penetration depth and sensitivity
of the SPR instrument were experimentally determined for the calculation
of nonspecific adsorption surface coverage. This provides a method
to better examine antifouling surface coatings and compare crossing
different coatings and experimental systems. Direct comparison of
antifouling performance of different diazonium salts was facilitated
by a tripad SPR sensor design. The electrografted 4-phenylalanine
diazonium chloride (4-APhe) layers with zwitterionic characteristic
demonstrate ultralow fouling
Improving Prediction of Peroxide Value of Edible Oils Using Regularized Regression Models
We present four unique prediction techniques, combined with multiple data pre-processing methods, utilizing a wide range of both oil types and oil peroxide values (PV) as well as incorporating natural aging for peroxide creation. Samples were PV assayed using a standard starch titration method, AOCS Method Cd 8-53, and used as a verified reference method for PV determination. Near-infrared (NIR) spectra were collected from each sample in two unique optical pathlengths (OPLs), 2 and 24 mm, then fused into a third distinct set. All three sets were used in partial least squares (PLS) regression, ridge regression, LASSO regression, and elastic net regression model calculation. While no individual regression model was established as the best, global models for each regression type and pre-processing method show good agreement between all regression types when performed in their optimal scenarios. Furthermore, small spectral window size boxcar averaging shows prediction accuracy improvements for edible oil PVs. Best-performing models for each regression type are: PLS regression, 25 point boxcar window fused OPL spectral information RMSEP = 2.50; ridge regression, 5 point boxcar window, 24 mm OPL, RMSEP = 2.20; LASSO raw spectral information, 24 mm OPL, RMSEP = 1.80; and elastic net, 10 point boxcar window, 24 mm OPL, RMSEP = 1.91. The results show promising advancements in the development of a full global model for PV determination of edible oils