Cross-Correlation of Optical Microcavity Biosensor Response with Immobilized Enzyme Activity. Insights into Biosensor Sensitivity

Abstract

Porous silicon multilayer structures have remarkable optical and morphological properties that can be exploited for biosensing. In particular, a high internal surface area (>100 m(2)/cm(3)) and a linear response profile to changes in the dielectric environment enable fabrication of sensitive devices and a straightforward quantitation of the optical response. These essential operating characteristics are illustrated for p+ mesoporous silicon (pore diameter 15-20 nm) optical microcavities. A series of devices were prepared to permit the immobilization of glutathione-S-transferase ( approximately 50 kDa) within the porous matrix. Enzyme activity was exploited as an indirect means to quantitate the amount of protein immobilized. Activity was positively correlated with the optical sensor response. However, at high enzyme load the activity becomes nonlinear while the microcavity response remains linear. These data were used to determine the transduction limit (minimum amount of protein required to transduce an optical response), which is reported as areal mass sensitivity ranging between 50 and 250 pg/mm(2). This value is considered in context with the dynamic range of the bulk sensitivity, defined as the magnitude of the wavelength shift per refractive index unit, which was measured as a function of microcavity design parameters. This work has uncovered key parameters that can be tuned to improve the detection limit of this sensor modality. Because of the ever increasing number of emerging new biosensor technologies, defining sensor detection limits has become an ambiguous topic and a need exists to standardize measurements and sensitivity units. For chip-based devices, it seems appropriate to report sensitivity in terms of the minimum number of grams of bound target per surface area.

Photonic Crystal-Based Sensors for Detecting Alcohol Concentration

“…As the increasing of ethanol concentration from 10% to 80%, the red shift for the 600˝C sintered TiO 2 sensor is 130 nm (see Table 2). According to Equations (4) and (5), the sensitivity value of the 600˝C sintered TiO 2 inverse opal sensors is approximate 9090 nm/RIU, which is higher than that of the LSPR (190 nm/RIU) [34] and the planar SPR technique (3100 to 8800 nm/RIU) [35]. The results show that it is possible to distinguish ethanol concentration in the range between 10% and 80%, if only the peak shift is taken into account.…”

Aminosilane functionalizations of mesoporous oxidized silicon for oligonucleotide synthesis and detection

“…After the electrochemical process, pore dimension was increased so as to favour the infiltration of biological matter by rinsing the 'as-etched' PSi microcavities in a KOH -ethanol solution (1.5 mM) for 15 min [14]. The devices were then thermally oxidized against uncontrolled environmental ageing and corrosion in alkaline solutions.…”

A new strategy for label-free detection of lymphoma cancer cells

“…A current density of 200 mA cm −2 for 1.2 s was applied to obtain low refractive index layers (nL = 1.542; dL = 125 nm) while a current density of 100 mA cm −2 was applied for 1.4 s for high refractive index layers (nH = 1.784; dH = 108 nm). After electrochemical process, pores dimension was increased so as to favor the infiltration of biological matter by rinsing the fresh-made PSi microcavity in a KOH ethanol solution (1.5 mM) for 15 min [21]. The structure was then thermally oxidized in pure O 2 by a two-step process: pre-oxidation at 400°C for 30 min followed by oxidation at 900°C for 15 min.…”