Modifying messages stored in mixtures of molecules using thin-layer chromatography

A method of reading data from a machine-readable medium, the method comprising:

• receiving an association between a set of digit/position pairs and at least a first and a second subsets of digit/position pairs;
• receiving a one-to-one association between at least the first subset of digit/position pairs and a first subset of molecules, and the second subset of digit/position pairs and a second subset of molecules, the first and the second subset of molecules selected from a set of unambiguously identifiable molecules, wherein each molecule in the first subset is identifiable by a first physical property, and each molecule in the second subset is identifiable by a second physical property, different from the first physical property;
• receiving a collection of molecules physically associated with a substrate of the machine-readable medium at an addressable location thereon, the collection comprising at least a first subcollection of molecules selected from the first subset of molecules, and a second subcollection of molecules, selected from the second subset of molecules;
• determining a numerical value comprising the set of digit/position pairs from the collection of molecules, wherein determining the numerical value comprises:
• setting each position of the first subset of digit/position pairs to the digit whose associated molecule is present in the first subcollection;
• setting each position of the second subset of digit/position pairs to the digit whose associated molecule is present in the second subcollection;
• and
• combining the first and the second subsets of digit/position pairs.