An apparatus for conducting a melting curve analysis of nucleic acids on a microarray by exciting a predefined portion of the microarray with a light beam and detecting emissions of fluorescent light comprising: an illuminator assembly, including a light source configured to produce the light beam, the light beam comprising electromagnetic radiation having one or more wavelengths, a band pass filter configured to eliminate wavelengths close to the wavelength of fluorescent light emitted from the nucleic acids, a mirror configured to reflect the light beam and to allow the fluorescent light emission to pass through, and an objective lens configured to focus the light beam on a predefined portion of the microarray, an emissions detector configured to sense emissions of fluorescent light from the predefined portion of the microarray, wherein the light beam produced by the light source and the emissions of fluorescent light are configured for transmission along a coincident path, a filuid circulation system, including a microarray cassette assembly including a frame including an opening configured to receive a microarray slide, the opening having a spacer disposed about an inside perimeter, a fluid inlet port, and a fluid outlet port, an optical window attached to the frame, a seal disposed on the frame opposite the optical window, wherein when a microarray slide is received within the opening, the spacer maintains the microarray slide separate from the optical window, the space between the microarray slide and the optical window defining a microarray chamber configured to allow the flow of fluid from the fluid inlet port to the fluid outlet port across the microarray slide, a pump configured to receive fluid from a fluid reservoir (52, 54) and to circulate the fluid through a fluid supply line coupled to a temperature-control assembly, and a fluid return line coupled to the fluid outlet port, wherein the temperature control assembly includes a temperature controller, a heat plate, a heater at a first heat plate side, a heater block at a second heat plate side, and a fluid heater, including a tubing wherein the tubing is disposed within a channel formed in the heater block, the tubing configured to allow the flow of fluid from the fluid supply line to the fluid inlet port, wherein the temperature of the fluid is brought to the temperature of the heater block by conduction through the tubing, wherein the heat plate is arranged to transfer the heat generated by the heater to the microarray through the heater block in direct contact with the microarray, and wherein the light beam and the micro array are movable relative to each other. an illuminator assembly, including a light source configured to produce the light beam, the light beam comprising electromagnetic radiation having one or more wavelengths, a band pass filter configured to eliminate wavelengths close to the wavelength of fluorescent light emitted from the nucleic acids, a mirror configured to reflect the light beam and to allow the fluorescent light emission to pass through, and an objective lens configured to focus the light beam on a predefined portion of the microarray, an emissions detector configured to sense emissions of fluorescent light from the predefined portion of the microarray, wherein the light beam produced by the light source and the emissions of fluorescent light are configured for transmission along a coincident path, a filuid circulation system, including a microarray cassette assembly including a frame including an opening configured to receive a microarray slide, the opening having a spacer disposed about an inside perimeter, a fluid inlet port, and a fluid outlet port, an optical window attached to the frame, a seal disposed on the frame opposite the optical window, wherein when a microarray slide is received within the opening, the spacer maintains the microarray slide separate from the optical window, the space between the microarray slide and the optical window defining a microarray chamber configured to allow the flow of fluid from the fluid inlet port to the fluid outlet port across the microarray slide, a pump configured to receive fluid from a fluid reservoir (52, 54) and to circulate the fluid through a fluid supply line coupled to a temperature-control assembly, and a fluid return line coupled to the fluid outlet port, wherein the temperature control assembly includes a temperature controller, a heat plate, a heater at a first heat plate side, a heater block at a second heat plate side, and a fluid heater, including a tubing wherein the tubing is disposed within a channel formed in the heater block, the tubing configured to allow the flow of fluid from the fluid supply line to the fluid inlet port, wherein the temperature of the fluid is brought to the temperature of the heater block by conduction through the tubing, wherein the heat plate is arranged to transfer the heat generated by the heater to the microarray through the heater block in direct contact with the microarray, and wherein the light beam and the micro array are movable relative to each other.