Molecular Biology on a Chip - Introduction to BioMEMS - page 245

and vibrate it and obtain the same mass balance sensitivities that can be obtained in vacuum.
However, human inventiveness seems endless. In 2003, Scott Manalis' group at MIT managed
to microfabricate a hollow cantilever (3-μm-thick luid layer) that can be illed with luids and
vibrated in vacuum (without spilling the luids into the vacuum!). Adsorption of the solutes
onto the inner walls of the cantilever alters the mass of the cantilever and changes its resonance
frequency (by a fraction of a percent, at ~200 kHz), which can be readily detected ( Figure 4.31 ).
his “suspended microchannel resonator” has also been used to measure the mass, density, and
size of particles, including cells in their normal life cycle. Sensitivity is highest near the cantile-
ver tip, enabling the measurement of particle masses with a precision of 300 ag (1 ag = 10 −18 g).
4.9 Summary
Microluidics is revolutionizing virtually every molecular biology technique. his revolution
is inevitable for two overlapping reasons: (1) microluidics allows for handling minute quanti-
ties of precious luids (which could be done previously with robotic pipetters), and (2) provides
dirt-cheap automation. Automated luid handling is a requisite to reduce human errors and
to perform high-throughput experimentation. Robotic pipetters are too costly for shrinking
university and research budgets and too bulky to be deployed in home care and ield settings.
Clearly, microluidics should become a winning technology.
FUTURE MICROFLUIDIC ASSAYS: THE “CAR
TREND” VERSUS THE “TOY TREND”
We see two diverging trends in the miniaturization of diagnostic devices (typi-
cally, microdevices that perform a few biochemical reactions), depending mostly on where
they will be used (and less by who will use them). For those systems for which there is no
incentive to be untethered from a laboratory wall, the trend is an increase in integration,
similar to what we have seen in the car industry in the last 25 years with the incorporation
of all the technologies from Formula 1: electronic chips now control almost every func-
tion of the car, from steering to braking, fuel injection, shiting, etc. Importantly, all these
technologies are hidden from the driver, providing a more pleasant experience. Similarly,
the end users of a microluidic system do not want to be bothered with the diiculties of
microvalves and micropumps, they want to be helped by them. When the device can be
used in a laboratory setting, in which it can be powered up with electricity, luids, and
pressurized gases, and can be placed on a computerized microscope stage for inspection,
the design can easily incorporate a range of power-hungry sensors and actuators. Ideally,
these systems should work by pushing buttons only and loading of luids into them should
be through open ports (“top-loadable”)—as an analogy, we would like their connections
to be as simple as a USB connector.
However, there is also a large class of diagnostics devices that cannot be tethered to
a wall—those that need to be portable so they can deployed to the ield. hese systems
need to be made the size of a disposable plastic credit card or, even better, a paper stamp.
hey cannot consume energy, or at best, they must run on batteries or solar cells. he
typical end user will be a patient who does not have a technical education and might
even have a physical disability, so the system should be really easy to use, like a toy. Note
that there is nothing wrong with the term “toy”—toys are safe, simple devices that help
us learn.