Biomedical Engineering Reference
In-Depth Information
11
Porous Silicon in Biosensing Applications
Benjamin L. Miller
CONTENTS
11.1 Introduction ......................................................................................................................271
11.2 Origins and Definitions ..................................................................................................272
11.3 PSi Biosensors: Early Work at Rochester ....................................................................274
11.4 From Empirical Observations to Predictable Behavior:
Understanding the Properties of Mesoporous Silicon
Biosensors in Greater Detail ..........................................................................................276
11.5 Using Enzyme Assays as a Secondary Monitor of Sensor Performance ................278
11.6 Studying the Longevity of PSi under Environmentally and
Physiologically Relevant Conditions ............................................................................283
11.7 PSi Biosensors in Hydrogels: Toward the “Smart Bandage” ....................................283
11.8 Beyond Mesoporous Silicon: Larger-Volume Structures ..........................................284
11.9 Alternative Sensing Modes and Device Structures ....................................................285
11.9.1 “Smart Dust” ......................................................................................................285
11.9.2 Electrical Sensors as an Alternative Biosensing Mechanism ......................286
11.10 Conclusions and Prospective ........................................................................................287
References ....................................................................................................................................288
11.1
Introduction
The detection of harmful microorganisms has undergone a considerable metamorphosis
since Hans Joachim Gram, a Danish physician, first observed, in the early 1860s, the capac-
ity of crystal violet to cause a certain class—but not another—of bacterium to acquire a
purplish color.
1
In particular, the explosive growth in our knowledge of the molecules that
make us and the organisms that might do us harm, through the parallel fields of
genomics,
2
proteomics,
3
and metabolomics,
4
has made improved detection methods both
possible and a necessity.
Microbiological analysis since the days of Gram has relied primarily on visual exami-
nation of cultures, cell staining, or antibody- or nucleic-acid-based assays that require sig-
nificant sample manipulation and “labeling” of the molecular target with a secondary
antibody, a fluorescent tag, or a radiolabel. Such methods have been enormously success-
ful in centralized diagnostic laboratories. However, with their requirements for expensive
271
