Pocket-Size Wireless Nanoelectrospray Ionization Mass Spectrometry for Metabolic Analysis of Salty Biofluids and Single Cells

Analysis of volume-limited biological samples such as
single cells
and biofluids not only benefits clinical purposes but also promotes
fundamental research in life sciences. Detection of these samples,
however, imposes strict requirements on measurement performance because
of the minimal volume and concentrated salts of the samples. Herein,
we developed a self-cleaning nanoelectrospray ionization device powered
by a pocket-size “MasSpec Pointer” (MSP-nanoESI) for
metabolic analysis of salty biological samples with limited volume.
The self-cleaning effect induced by Maxwell–Wagner electric
stress helps with keeping the borosilicate glass capillary tip free
from clogging and thus increasing salt tolerance. This device possesses
a high sample economy (about 0.1 μL per test) due to its pulsed
high voltage supply, sampling method (dipping the nanoESI tip into
analyte solution), and contact-free electrospray ionization (ESI)
(the electrode does not touch the analyte solution during ESI). High
repeatable results could be acquired by the device with a relative
standard deviation (RSD) of 1.02% for voltage output and 12.94% for
MS signals of caffeine standard. Single MCF-7 cells were metabolically
analyzed directly from phosphate buffered saline, and two types of
untreated cerebrospinal fluid from hydrocephalus patients were distinguished
with 84% accuracy. MSP-nanoESI gets rid of the bulky apparatus and
could be held in hand or put into one’s pocket for transportation,
and it could operate for more than 4 h without recharge. We believe
this device will boost scientific research and clinical usage of volume-limited
biological samples with high-concentration salts in a low-cost, convenient,
and rapid manner.