An optrode particle geometry to decrease response time.

A hollow 3 μm sensing microcapsule containing chromoionophores within a 100 nm organosilica shell is reported. This shows a response to an ion step two orders of magnitude faster than 'filled' sensing particles of similar diameter. Incorporation of chromoionophores ETH 5294 and ETH 7061 in the capsule shell is shown with a t(90) response <2 s compared with >15 min for filled particles of similar diameters. This ultrafast geometry is also extended to dual ionophore dye incorporation and preliminary exploration of a FRET-based ratiometric method is examined to extend the pH response range, using a single excitation wavelength.