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Flow-Through Porous Silicon Membranes for Real-Time Label-Free Biosensing
Authors:
Yiliang Zhao,
Girija Gaur,
Scott T. Retterer,
Paul E. Laibinis,
Sharon M. Weiss
Abstract:
A flow-through sensing platform based on open-ended porous silicon (PSi) microcavity membranes that are compatible with integration in on-chip sensor arrays is demonstrated. Due to the high aspect ratio of PSi nanopores, the performance of closed-ended PSi sensors is limited by infiltration challenges and slow sensor responses when detecting large molecules such as proteins and nucleic acids. In o…
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A flow-through sensing platform based on open-ended porous silicon (PSi) microcavity membranes that are compatible with integration in on-chip sensor arrays is demonstrated. Due to the high aspect ratio of PSi nanopores, the performance of closed-ended PSi sensors is limited by infiltration challenges and slow sensor responses when detecting large molecules such as proteins and nucleic acids. In order to improve molecule transport efficiency and reduce sensor response time, open-ended PSi nanopore membranes were used in a flow-through sensing scheme, allowing analyte solutions to pass through the nanopores. The molecular binding kinetics in these PSi membranes were compared through experiments and simulation with those from closed-ended PSi films of comparable thickness in a conventional flow-over sensing scheme. The flow-through PSi membrane resulted in a six-fold improvement in sensor response time when detecting a high molecular weight analyte (streptavidin) versus in the flow-over PSi approach. This work demonstrates the possibility of integrating multiple flow-through PSi sensor membranes within parallel microarrays for rapid and multiplexed label-free biosensing.
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Submitted 15 July, 2016;
originally announced July 2016.
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Optical Response of Monolayer CdTe/CdS Quantum Dots to X-rays and Gamma-rays
Authors:
Girija Gaur,
Dmitry S. Koktysh,
Daniel M. Fleetwood,
Robert A. Weller,
Robert A. Reed,
Bridget R. Rogers,
Sharon M. Weiss
Abstract:
We investigate the influence of X-ray and gamma-ray irradiation on the photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs) immobilized in porous silica (PSiO2) scaffolds. The highly luminescent QD-PSiO2 thin films allow for straightforward monitoring of the optical properties of the QDs through continuous wave and time-resolved photoluminescence spectroscopy. The PSiO2 host matri…
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We investigate the influence of X-ray and gamma-ray irradiation on the photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs) immobilized in porous silica (PSiO2) scaffolds. The highly luminescent QD-PSiO2 thin films allow for straightforward monitoring of the optical properties of the QDs through continuous wave and time-resolved photoluminescence spectroscopy. The PSiO2 host matrix itself does not modify the QD properties. X-ray irradiation of the QD-PSiO2 films in air leads to an exponential decrease in QD emission intensity, an exponential blue-shift in peak emission energy, and substantially faster exciton decay rates with increasing exposure doses from 2.2 Mrad(SiO2) to 6.6 Mrad(SiO2). Gamma-ray irradiation of a QD-PSiO2 thin film at a total exposure dose of 700 krad(SiO2) in a nitrogen environment results in over 80% QD photodarkening but no concurrent blue-shift in peak emission energy due to a lack of photo-oxidative effects. Near-complete and partial reversal of irradiation-induced photodarkening was demonstrated on X-ray and gamma-ray irradiated samples, respectively, through the use of a surface re-passivating solution, suggesting that there are different contributing mechanisms responsible for photodarkening under different irradiation energies. This work contributes to improving the reliability and robustness of QD based heterogeneous devices that are exposed to high risk, high energy environments with the possibility of also developing QD-based large area, low-cost, re-useable, and flexible optical dosimeters.
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Submitted 21 August, 2015;
originally announced August 2015.
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Interfacial Effects on the Optical Properties of CdTe/CdS Quantum Dots
Authors:
Girija Gaur,
Dmitry S. Koktysh,
Daniel M. Fleetwood,
Robert A. Weller,
Robert A. Reed,
Sharon M. Weiss
Abstract:
Using a combination of continuous wave and time-resolved spectroscopy, we study the effects of interfacial conditions on the radiative lifetimes and photoluminescence intensities of colloidal CdTe/CdS quantum dots (QDs) embedded in a three-dimensional nanostructured silicon (NSi) matrix. The NSi matrix was thermally oxidized under different conditions to change the interfacial oxide thickness. QDs…
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Using a combination of continuous wave and time-resolved spectroscopy, we study the effects of interfacial conditions on the radiative lifetimes and photoluminescence intensities of colloidal CdTe/CdS quantum dots (QDs) embedded in a three-dimensional nanostructured silicon (NSi) matrix. The NSi matrix was thermally oxidized under different conditions to change the interfacial oxide thickness. QDs embedded in a NSi matrix with ~0.5 nm of interfacial oxide exhibited reduced photoluminescence intensity and nearly five times shorter radiative lifetimes (~16 ns) compared to QDs immobilized within completely oxidized, nanostructured silica (NSiO2) frameworks (~78 ns). Optical absorption by the sub-nm oxidized NSi matrix partially lowers QD emission intensities while non-radiative carrier recombination and phonon assisted transitions influenced by defect sites within the oxide and NSi are believed to be the primary factors limiting the QD exciton lifetimes in the heterostructures.
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Submitted 23 April, 2015;
originally announced April 2015.