obtaining a plurality of different Raman-active dots each comprising a nanoparticle containing a plurality of Raman tags incorporated therein, the plurality of Raman tags having multiple peaks in a Raman shift region of 400-1600 cm⁻¹;

exposing cells of a sample to the plurality of different Raman-active dots;

causing the sample and the plurality of different Raman-active dots to flow through a microfluidic channel of a flow cytometer through which a laser beam passes, wherein the laser beam is generated by a single excitation laser;

detecting Raman signals emitted from the Raman tags of the plurality of different Raman-active dots while being illuminated by the single laser beam; and

measuring characteristics of the cells based on the detected Raman signals;

wherein the plurality of different Raman tags are each generated by (i) substituting hydrogens in a tetraene unit of a cyanine dye by deuterium and (ii) introducing at least one substituent to an IR740 skeleton at a respective one of a plurality of different positions without changing an absorption wavelength of the cyanine dye, the at least one substituent comprising Chlorine, Bromine, or Fluorine.

a first laser source comprising a single excitation laser configured to generate a single laser beam;

a flow cytometer comprising a microfluidic channel through which a fluid flows, the fluid comprising a plurality of cells suspended therein that are labeled with a plurality of different Raman-active dots, each said Raman-active dot comprising a nanoparticle containing a plurality of Raman tags incorporated therein, the plurality of Raman tags having multiple peaks in a Raman shift region of 400-1600 cm⁻¹;

a detector configured to detect Raman signals emitted from the Raman tags of the plurality of different Raman-active dots while being illuminated by the single laser beam as the single laser beam passes through the microfluidic channel; and

a computing device configured to determine characteristics of the plurality of cells based on the detected Raman signals;

wherein the plurality of different Raman tags are each generated by (i) substituting hydrogens in a tetraene unit of a cyanine dye by deuterium and (ii) introducing at least one substituent to an IR740 skeleton at a respective one of a plurality of different positions without changing an absorption wavelength of the cyanine dye, the at least one substituent comprising Chlorine, Bromine, or Fluorine.