  Improving direct detection capability close to the star through improved
star-subtraction and post-processing techniques is vital for discovering new
low-mass companions and characterizing known ones at longer wavelengths. We
present results of 17 binary star systems observed with the Magellan Adaptive
Optics system (MagAO) and the Clio infrared camera on the Magellan Clay
Telescope using Binary Differential Imaging (BDI). BDI is an application of
Reference Differential Imaging (RDI) and Angular Differential Imaging (ADI)
applied to wide binary star systems (2\arcsec $<\Delta \rho<$ 10\arcsec) within
the isoplanatic patch in the infrared. Each star serves as the
point-spread-function (PSF) reference for the other, and we performed PSF
estimation and subtraction using Principal Component Analysis. We report
contrast and mass limits for the 35 stars in our initial survey using BDI with
MagAO/Clio in L$^\prime$ and 3.95$\mu$m bands. Our achieved contrasts varied
between systems, and spanned a range of contrasts from 3.0-7.5 magnitudes and a
range of separations from 0.2\arcsec to $\sim$2\arcsec. Stars in our survey
span a range of masses, and our achieved contrasts correspond to late-type M
dwarf masses down to $\sim$10 M$_{\rm{jup}}$. We also report detection of a
candidate companion signal at 0.2\arcsec (18 AU) around HIP 67506 A (SpT G5V,
mass $\sim$1.2\Msun), which we estimate to be ~60-90 M$_{\rm{jup}}$. We found
that the effectiveness of BDI is highest for approximately equal brightness
binaries in high-Strehl conditions.
