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A NOVEL APPROACH TO MAGNETIC FIELD BIOSENSORS
NMR AND SQUID DETECTION
A. Valsesiaa, P. Colpoa, F. Rossia, P. Arosiob,
M. Marianic,d, M. Cortic, d, M.F. Casulae, A.
Lascialfarib,c, d a European Commission, Joint
Research Center, IHCP, Ispra (VA), Italy b
Department of Molecular Sciences Applied to
Biosystems - DISMAB , Università degli Studi di
Milano, Milano, Italy c Department of Physics
Volta, University of Pavia, Pavia, Italy d
S3-CNR-INFM, Modena, Italy e Dipartimento di
Scienze Chimiche, Università di Cagliari,
Cagliari, Italy
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Introduction
We have studied novel approaches for the
realization of Magnetic Field Effect Biosensors
(MFBs), by optimizing the technique of
immobilization of biomolecular probes on the
surface and in the bulk. By using maghemite
nanoparticles for marking the biomolecules, we
obtained a good sensitivity of the detection
method of MFBs using Nuclear Magnetic Resonance
(NMR) and SQUID.
MFBs Approach 1

• Plasma Deposited Poly Acrylic Acid (ppAA) 1
• Adsorption of human IgG
• Blocking of the unreacted surface groups by BSA
• Reaction with biotinated Ab-IgG molecules at
  different concentrations
• Absorption of streptavidin
• Absorption of biotinated modified ?-Fe2O3
  superparamagnetic nanoparticles 2

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Magnetization Measurements
SQUID
QCM test

• QCM measurements
• Frequency shift as a function of the biotinated
  Ab-IgG molecules concentration
• SQUID measurements
• Room temperature
• Constant magnetic field H 500 Oe

Magnetic data depend on the concentration of
Ab-IgG molecules blocked on the surface. The
magnetic moment increases in presence of ?-Fe2O3
with respect to the substrate (protein) probe.
This represents the method of detection on which
MFB ( biochips ! ) are based. ! Specific
biological recognition !
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MFBs Approach 2
Streptavidin

• Hydrogel of Agarose (1) directly prepared in
  the glass tube for NMR measurements
• Diffusion of biotinated modified ?-Fe2O3
  superparamagnetic nanoparticles with mild shaking
  
• Diffusion of streptavidin with mild shaking

Agarose
NMR Measurements (preliminary results)
Fe2O3-c-PMA-c-Biotin

• 1H-NMR relaxation times of the Agarose gel
• at 20.1 MHz T1 2.92 sec. T2 98 msec.
• at 41 MHz T1 2.90 sec. T2 103 msec.

• Room temperature
• 1H-NMR relaxation times T1 and T2 evaluated at
  20.1 and 41 MHz as a function of time after the
  addition of streptavidin in Agarose gel where
  biotinated modified ?-Fe2O3 superparamagnetic
  nanoparticles were included
• Different relaxation times adding streptavidin
  with respect to np-hydrogel gt
• Sensitivity of NMR
• The longitudinal relaxation time T1 is weakly
  influenced by addition of streptavidin to gel
  with biotinated modified ?-Fe2O3 but ..
• a 10-15 change of the transverse relaxation time
  T2 ? method of detection of probe-analyte
  interaction

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Concluding remarks Two different novel approaches
for the realization of Magnetic Field Effect
Biosensors (MFBs) based on SQUID magnetometry and
Nuclear Magnetic Resonance detection were
developed. Immobilizing biomolecular probe on
functionalized surface ( BIOCHIPS ! ), the
specific biological recognition
biotin-streptavidin was obtained by means of
SQUID magnetic measurements. Very interesting
perspectives using 1H-NMR detection technique on
bulk probes were presented.
1 F. Bretagnol, A. Valsesia, G. Ceccone, P.
Colpo, D. Gilliland, L. Ceriotti, M. Hasiwa, and
F. Rossi Plasma Processes and Polymers 3, 443
(2006). 2 C. J. Lin, R. A. Sperling, J. K. Li,
T. Yang, P. Li, M. Zanella, W. H. Chang, and W.
J. Parak Small 4, 334 (2008).
Acknowledgments Fondazione Cariplo is gratefully
acknowledged for having funded the project