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Ca 2+ is among the most important intracellular second messengers participating in a plethora of biological processes, and the measurement of Ca 2+ fluctuations is significant in the phenomenology of the underlying processes. Aequorin-based Ca 2+ probes represent an invaluable tool for reliable measurement of Ca 2+ concentrations and dynamics in different subcellular compartments. However, their use is limited due to the lack on the market of ready-to-use, cost-effective, and portable devices for the detection and readout of the low-intensity bioluminescence signal produced by these probes. Silicon photomultipliers (SiPMs) are rapidly evolving solid-state sensors for low light detection, with single photon sensitivity and photon number resolving capability, featuring low cost, low voltage, and compact format. Thus, they may represent the sensors of choice for the development of such devices and, more in general, of a new generation of multipurpose bioluminescence detectors suitable for cell biology studies. Ideally, a detector customized for these purposes must combine high dynamic range with high fidelity in reconstructing the light intensity signal temporal profile. In this article, the ability to perform aequorin-based intracellular Ca 2+ measurements using a multipurpose, low-cost setup exploiting SiPMs as the sensors is demonstrated. SiPMs turn out to assure performances comparable to those exhibited by a custom-designed photomultiplier tube-based aequorinometer. Moreover, the flexibility of SiPM-based devices might pave the way toward routinely and wide scale application of innovative biophysical protocols.

Bioluminescence detection requires single-photon sensitivity, extremely low detection limits and wide dynamic range. Such performances were traditionally assured by photomultiplier-tubes based systems. However, development of novel applications and industrialization call for the introduction of more robust, compact and scalable devices. Silicon photomultipliers were recently put forward as the alternative to phototubes for a new generation of flexible and user friendly instruments. In this article, the figures of merit of a siliconphotomultiplier based system relying on a compact, low cost system are investigated. Possible implementations are proposed and a proof-of-principle bioluminescence measurement is performed.

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No abstract