  We introduce a dark energy-modified minimum length uncertainty relation
(DE-MLUR) or dark energy uncertainty principle (DE-UP) for short. The new
relation is structurally similar to the MLUR introduced by K{\' a}rolyh{\' a}zy
(1968), and reproduced by Ng and van Dam (1994) using alternative arguments,
but with a number of important differences. These include a dependence on the
de Sitter horizon, which may be expressed in terms of the cosmological constant
as $l_{\rm dS} \sim 1/\sqrt{\Lambda}$. Applying the DE-UP to both charged and
neutral particles, we obtain estimates of two limiting mass scales, expressed
in terms of the fundamental constants $\left\{G,c,\hbar,\Lambda, e\right\}$.
Evaluated numerically, the charged particle limit corresponds to the order of
magnitude value of the electron mass ($m_e$), while the neutral particle limit
is consistent with current experimental bounds on the mass of the electron
neutrino ($m_{\nu_e}$). Possible cosmological consequences of the DE-UP are
considered and we note that these lead naturally to a holographic relation
between the bulk and the boundary of the Universe. Low and high energy regimes
in which dark energy effects may dominate canonical quantum behaviour are
identified and the possibility of testing the model using near-future
experiments is briefly discussed.
