Methods, reagents, and substrates for detecting target analytes

A method for detecting a plurality of target analytes, the method comprising:

• forming a first sandwich complex on a first paper substrate comprising a first target analyte from a sample and one or more first metal particles, and forming a second sandwich complex on a second paper substrate comprising a second target analyte from the sample and one or more second metal particles, wherein the first paper substrate is layered on top of the second paper substrate;
• directing a laser emission from a laser source onto the first sandwich complex on the first paper substrate such that the laser emission causes the one or more first metal particles associated with the first sandwich complex to produce a first emission signal while also ablating at least a portion of the first paper substrate to expose at least a portion of the second paper substrate that comprises the second sandwich complex such that the laser emission also causes the one or more second metal particles associated with the second sandwich complex to produce a second emission signal;
• and
• detecting the first emission signal from the first sandwich complex on the first paper substrate, the first emission signal being indicative of presence of the first target analyte and detecting the second emission signal from the second sandwich complex on the second paper substrate, the second emission signal being indicative of presence of the second target analyte.