Biomedical Engineering Reference
In-Depth Information
BSA
Measure reflectivity
of fluorescent
particles
Goat
antirabbit
750 nm-encoded
(Fluorescent)
400
500
600
nm
700
800
1)Rat albumin
(2) Rabbit
Antirat
Measure reflectivity
of non fluorescent
particles
540 nm-encoded
400
500
600
nm
700
800
FIGURE 11.14
Sailor “smart dust” experiment.
been observed.
48
Recently, the Fauchet laboratory has begun exploring the potential of
employing the electrical properties of macroporous Si in sensing charged molecules such
as DNA.
49
Thick layers of macroporous silicon were electrochemically etched in HF or
dimethylformamide; the resulting devices were attached to a computer-controlled induc-
tance-capacitance-resistance (LCR) meter. DNA probes were then introduced into the
device and allowed to adhere electrostatically, and measurements of changes in imped-
ance and phase angle were made while the sample was still wet. Results indicated that the
sensor could reproducibly detect complementary DNA, with good selectivity for the
“matched” sequence relative to fully “mismatch” sequence. The results fit well with a
“space charge region modulation” (SCRM) model;
50
binding of charged complementary
DNA to the electrostatically immobilized probe oligonucleotide alters both the dielectric
constant inside the pores, and the charge distribution of the underlying silicon itself. While
significant development work remains here to establish the sensitivity and generality of
electrical biosensors based on PSi, the potential simplicity of integrating such sensors with
microelectronics using standard fabrication techniques makes them highly attractive.
51
11.10
Conclusions and Prospective
Clearly, significant work remains to be done if PSi biosensors are to evolve from being an
area of academic research to a generally available detection (or diagnostic) tool.
Standardized methods for producing devices will be important, as will improved meth-
ods for device stabilization and probe immobilization. Little is known at this point regard-
ing long-term stability of biopolymer-functionalized devices; for example, does PSi
immobilization
enhance
or
retard
degradation of nucleic acids, peptides, and antibodies in
ambient conditions? Multianalyte (arrayed) sensors are an important goal, as are optical
and electrical sensors integrated with microfluidics, other sample preparation modules,
and “on-chip” detectors.
