Embodiments of the present invention relate to devices and methods for detecting cellular products using detection particles having product-specific detection reagents and having a characteristic spectral feature. In particular, devices and methods are provided for measuring secreted cellular products including cytokines. Detection substrates, include microwells having product-specific capture reagents thereon or comprising hydrophobic membranes are described having greater capability to detect products from individual cells in a mixture of heterogeneous cells. With the use of multiple detection particles, multiple cellular products can be detected in a single well. Additionally, using the inherent spectral properties of detection particles, no enzymatic reactions are needed to visualize a secreted product, thereby increasing the sensitivity, reproducibility and ease of use.