posted on 2016-08-31, 00:00authored byVadim Krivitsky, Marina Zverzhinetsky, Fernando Patolsky
The
detection of biomolecules is critical for a wide spectrum of applications
in life sciences and medical diagnosis. Nonetheless, biosamples are
highly complex solutions, which contain an enormous variety of biomolecules,
cells, and chemical species. Consequently, the intrinsic chemical
complexity of biosamples results in a significant analytical background
noise and poses an immense challenge to any analytical measurement,
especially when applied without prior efficient separation and purification
steps. Here, we demonstrate the application of antigen-dissociation
regime, from antibody-modified Si-nanowire sensors, as a simple and
effective direct sensing mechanism of biomarkers of interest in complex
biosamples, such as serum and untreated blood, which does not require
ex situ time-consuming biosample manipulation steps, such as centrifugation,
filtering, preconcentration, and desalting, thus overcoming the detrimental
Debye screening limitation of nanowire-based biosensors. We found
that two key parameters control the capability to perform quantitative
biomarkers analysis in biosamples: (i) the affinity strength (koff rate) of the antibody–antigen recognition
pair, which dictates the time length of the high-affinity slow dissociation
subregime, and (ii) the “flow rate” applied during the
solution exchange dissociation step, which controls the time width
of the low-affinity fast-dissociation subregime. Undoubtedly, this
is the simplest and most convenient approach for the SiNW FET-based
detection of antigens in complex untreated biosamples. The lack of
ex situ biosample manipulation time-consuming processes enhances the
portability of the sensing platform and reduces to minimum the required
volume of tested sample, as it allows the direct detection of untreated
biosamples (5–10 μL blood or serum), while readily reducing
the detection cycle duration to less than 5 min, factors of great
importance in near-future point-of-care medical applications. We believe
this is the first ever reported demonstration on the real-time, direct
label-free sensing of biomarkers from untreated blood samples, using
SiNW-based FET devices, while not compromising the ultrasensitive
sensing capabilities inherent to these devices.