Biomedical Engineering Reference
In-Depth Information
BEADS, THE NEW PDMS?
In fact, David Walt's bead-based approach
can hardly be categorized as a “MEMS-
based” approach (none of its components require miniaturization), so why is it featured in
a BioMEMS book? Precisely because this approach manipulates miniature components for
biological applications (the stated subject of the topic), and it was revolutionary at that.
Historically speaking, David Walt's story has an interesting parallel in that, once
more in the ield of BioMEMS, another “outsider” (also a chemist working in Cambridge,
Massachusetts) brought a radical new solution that lowered costs and enabled new fron-
tiers, as George Whitesides had done with the introduction of PDMS in a silicon-based
arena. And now, every engineer must at least consider this sensing design for high-
throughput applications, just like every engineer will consider PDMS as a material for
building a microdevice.
his sends a clear message to our young researchers (as creativity declines with age,
there is little point in reminding the older generation, myself included): please think out-
side of the box!—whether the box is inside or outside Cambridge.
4.6.1.5 Electroaddressable Deposition of DNA and Protein
In 2007, Susan Brozik's group at Sandia National Laboratories developed what seems to be the
ultimate convenient scheme for depositing DNA and detecting hybridization (
Figure 4.17
):
the deposition is electroaddressable and hybridization is electrochemically detectable (so it
requires neither optical equipment nor biochemical reagents). For the same price, in addition,
it also allows for the deposition of proteins. Simultaneous electrochemical detection of a DNA
sequence related to the breast cancer BRCA1 gene and the human cytokine protein interleu-
kin-12 was demonstrated.
In certain settings (such as a biological laboratory), however, electrical addressability may not
be as important an advantage as optical readability (which can be performed with microscopes).
+ e
-
, - N
2
EDC/NHS/DNA
COOH
Step 1
Electrodes
1, 3, 5, 7, 9
N
+
N
+ e
-
, - N
2
Step 2
Electrodes
2, 4, 6, 8
N
+
N
FIGURE 4.17
Electroaddressable. deposition. of. DNA. and. protein.. (From. Jason. C.. Harper,. Ronen.
Polsky,.David.R..Wheeler,.Shawn.M..Dirk,.and.Susan.M..Brozik,.“Selective.immobilization.of.dna.and.
antibody.probes.on.electrode.arrays:.Simultaneous.electrochemical.detection.of.DNA.and.protein.on.
a.single.platform,”.
Langmuir
.23,.8285-8287,.2007..Figure.contributed.by.Susan.Brozik.)
