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ANALYTICAL CURRENTS
Monitoring live-cell secretion Robert Kennedy and colleagues at the University of Michigan have designed a microfluidic device that can quantitatively monitor secretions from live cells over time. The device could be useful for studying the secretory processes of live cells, and it could have applications in drug development.
Labeled insulin
Waste
Antibody
Kennedy and colleagues previously developed a microfluidic device that could detect insulin release by single islets of Langer-
Gate
Islet
hans (Anal. Chem. 2003, 75, 4711–4717). However, the device
Perfusion inlet
lacked a way to continuously flow solutions through the sample chamber. This limitation imposed restrictions on monitoring secretions over time and observing behavioral changes of the islet cells in response to drugs and other chemicals. The viability of
A microfluidic device that is 2.5 7.5 cm in size has been developed to monitor the secretion of insulin over time. (Adapted with permission. Copyright 2004 Royal Society of Chemistry.)
the cells was also limited because fresh nutrients weren’t consecretion over time in response to the glucose concentration.
tinuously supplied. The device has now been modified so that the islet cells in the
The investigators also monitored the behavior of the islet cells
sample chamber can be provided with fresh media and solutions
with different types of buffers, showing that the immunoassay for
through an inlet perfusion channel, into which fluid is pumped by
detecting insulin in the device is compatible with more than one
gas-driven pressure. The investigators determined that the de-
type of solution. However, precipitation of salts from certain types
tection of insulin is unperturbed by the perfusion of solutions and
of buffers can block the microchannels. Kennedy and colleagues showed that their device can be
that the cells are not damaged by fluid flow. Kennedy and colleagues next demonstrated that insulin se-
cleaned and re-used. And although the investigators use their
cretions from individual islets can be monitored as the glucose
device to monitor insulin secretion by islet cells, they point out
concentration is altered between 3 and 11 nM. The device’s de-
that with minor changes, it is amenable for studies of other cell
tection limits are sensitive enough to track oscillations in insulin
types. (Lab on Chip 2004, doi 10.1039/B404974H)
Array detector for LA-ICPMS The use of laser ablation (LA) as a sample-introduction method for inductively coupled plasma MS (ICPMS) allows for the direct analysis of a wide range of solid samples. However, shot-to-shot variations in the laser power and interactions between the laser and the sample can cause erratic responses, which make quantification difficult. To overcome these limitations, Gary Hieftje and colleagues at Indiana University, the University of Arizona, and the Pacific Northwest National Laboratory 302 A
have developed a new array detector for LA-ICPMS that detects multiple elements simultaneously. Simultaneous detection is used to eliminate the noise that is characteristic of the ablation process. Variations in the laser can be corrected for by normalizing the signal for each m/z value to the total ion signal. As a result, analyses can be performed with single laser pulses. This benefit leads to improved depth resolution, less sample consumption, and better precision.
A N A LY T I C A L C H E M I S T R Y / S E P T E M B E R 1 , 2 0 0 4
Using the new detector combined with a LA sample-introduction system, an ICP ionization source, and a Mattauch–Herzog mass spectrograph, the researchers achieved detection limits in the tens to hundreds of femtograms range and an isotope-ratio precision better than 0.02% RSD, with an integration period of 1 h. The instrument also performed depth-profile analysis with a depth resolution of 5 nm per ablation event. ( J. Am. Soc. Mass Spectrom. 2004, 15, 769–776)
