Abstract: The invention relates to methods and systems for use of bio-discs in quantifying an amount or concentration of one or more substances that are present in a biological sample. The system includes an optical disc having one or more samples deposited thereon, an optical element configured to emit and divert radiation onto the samples and components for measuring spectral change of the compound and determining an amount or concentration of one or more target substances. The bio-disc is prepared using a method including providing a membrane that is or can be dimensional to fit within a channel of the bio-disc, applying a reagent on the membrane which is configured to allow the reagent to be released from the membrane into a solution in contact with the membrane, and depositing the membrane in a channel of the bio-disc.