Wednesday, December 14, 2005

SMRs - Suspended Microfluidic Resonant sensors / detectors

Curious devices these are, using mems techniques to make suspended microfluidic channel resonators. These devices integrate a microfluidic biochemical / protein concentrator structure directly coupled to a MEMS suspended microfluidic channel - cantilever resonator, for mass balance detection of detected material.

Similar to a more conventional QCM - quartz crystal oscillator mass shift detection, but with the added twist of suitablity to biochemistry applications of wet chem detection - biomedical and biochemical.

Apparently the devices protoyped to date by Manalis' group in MIT have not yet yielded any (public) detection sensitivity advance over more conventional QCM mass balance detection - for reasons unknown.

A couple of thoughts I had relate to the sensitivity challenges -

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1] that pressurized microfluidic flows ( if pressurized from the coupled integrated fluidic biochemical concentrators ) might stiffen the suspended microchannel cantelevers in unpredictable ways, and

2] that the signal to noise of the sub 100Khz resonators might not be optimal - which if the present structures are retained, might gain benefit from the methods used in the more advanced recent design Inficon QCM thin film thickness rate controllers - by using a transmitted and received pulse train for the detection of the mass shift, rather than a quasistatic excitation.

Inficon's more novel QCM thin film thickness monitors, employ a patented method to send out a pulse train waveform near resonance, and cleanly detects a reflected pulse train (while not transmitting) to interrogate for phase and amplitude detection - with NO CW excitation of the QCM crystal.

In some sense this is very close to the techniques used in Acoustic microscopy - with some variation that the acoustic path length / time delay is nominally fixed in a sensor interogation, versus acoustic microscopy application.

Apparently Inficon's novel QCM signal methods have useful benefits to resolvable minimum detectable mass change in the Inficon thin film controller / monitor.

How this might be analogously implemented in SMRs of Manalis is something to think about, and as to whether the Inficon methods might benefit the S/N or detectable sensitivity of the novel SMR, and if it is possible to do at all.

Something to ponder.

UPDATE - Feb 3rd 2006
- come to think of it, if the SMR is operated discrete stopped flow, the pressure stiffening / desensitizing concern can be alleviated by stopped flow, and interleaved resonance interrrogation. By depressurizing the microchannel, any pressure stiffening can be eliminated as a sensitivity concern, although pressure decay relaxation time constant might slow the Quasi Real Time Performance. AHA !

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