  By applying an idea of Borodin and Olshanski [J. Algebra 313 (2007), 40-60],
we study various scaling limits of determinantal point processes with trace
class projection kernels given by spectral projections of selfadjoint
Sturm-Liouville operators. Instead of studying the convergence of the kernels
as functions, the method directly addresses the strong convergence of the
induced integral operators. We show that, for this notion of convergence, the
Dyson, Airy, and Bessel kernels are universal in the bulk, soft-edge, and
hard-edge scaling limits. This result allows us to give a short and unified
derivation of the known formulae for the scaling limits of the classical random
matrix ensembles with unitary invariance, that is, the Gaussian unitary
ensemble (GUE), the Wishart or Laguerre unitary ensemble (LUE), and the MANOVA
(multivariate analysis of variance) or Jacobi unitary ensemble (JUE).
