A time-gated fluorescence detector using a tuning fork chopper

We describe an affordable gated fluorescence detection system to measure fluorescent compounds with long-lifetimes that uses a tuning fork chopper to block the intense excitation pulse from a flash lamp or short-lived fluorescence. A conventional non-gated inexpensive photosensor module is used to collect the luminescence signal. Using the long-lived luminescence from the terbium(III)-dipicolinic acid (DPA) chelate, we demonstrate a limit of detection (LOD) of 120 pM for DPA. This system is not only an order of magnitude less expensive than an electronically gateable phototomultiplier tube (GPMT), it exhibits no evidence of gradual loss of sensitivity, due likely to photocathode fatigue and deterioration, observed with a GPMT