Nanoparticle structures with barcodes

A library of barcoded particle populations, comprising

• barcoded particles that are composite particles comprising at least one type of inorganic fluorescent nanoparticle selected from a list of N types of inorganic fluorescent nanoparticles, these inorganic fluorescent nanoparticles being encapsulated in an inorganic material and N being an integer greater than or equal to 3;
• each population is defined by an N-tuple, wherein the element i of the N-tuple is the weight fraction of type i of inorganic fluorescent nanoparticle in the composite particles, defining a fluorescence spectrum I(C1, . . . , Ci, . . . CN)(λ) for that population;
• each type of the N types of inorganic fluorescent nanoparticles is encapsulated in at least one population;
• at least one population of the inorganic fluorescent nanoparticles in the composite particles has a weight fraction that is greater than or equal to 1%;
• and
• at least one type of inorganic fluorescent nanoparticle is encapsulated in at least two populations with different weight fractions.