# Nanoplasmonic Sensor Based on Surface Plasmon-Coupled Emission: Review
## 8 Application of SPCE for Detection of Molecules  
Fluorescence-based sensor is a significant and sensitive instrument for the detection of chemical material and biomolecules [41]. The SPCE-based sensors are devices that work by the interaction of surface plasmon and emission from fluorophores. Monitoring of biological interaction, display of the diagnostic signal, detection of glucose, oxygen, carbon dioxide, DNA, and toxic chemical are the subjects in the area of sensing and biosensing. The significant parameters are sensitivity, selectivity, response time and repeatability. The advantages of SPCE-based sensors include small volume for detection of chemical and biochemical materials, low background noise, and high-sensing limitations. Thus, a combination of fluorescence and SPR can provide a significant method of overcoming the limitations of other methods used in sensing the biomolecules and toxic chemicals. The SPCE was used to detect the oxygen using ruthenium dye, and the response time was about 100 ms. The sensor was inexpensive and highly sensitive for the detection and recognition of the low concentration of oxygen [43]. In 2012, [PERSON] et al. used SPCE to detect the heavy metals and found that the SPCE of semiconductor quantum dots (QD), such as CdTe-QD, is adequately sensitive to recognize the mercury ions. They used the synthesis of the CdTe-QD in solution form attaching it to a gold layer and the limit of detection was 0.23 nmol L\({}^{-1}\)[44]. In 2013, [PERSON] et al. utilized the silver-\(\alpha\) nano alumina thin film hybrids as a sensing layer for detection of heavy metals. They arranged the reverse Kretschmann setup and exited the fluorophores using laser at 532 nm, and succeeded in measuring 1 \(\upmu\)M concentration of Cd\({}^{2+}\)[45]. The SPCE is a merit method to evaluate an antigen or an antibody as immunoassay. Immunoassay based on fluorescence spectroscopy is highly interesting method in biosensing [46; 47] and medical diagnostics [37]. Immunoassay based on fluorescence is a sensitive and accurate method, but it has high background fluorescence and interaction with the signal [48]. The SPCE is an approach to overcome the interference of fluorescence signal with background fluorescence. In 2004, [PERSON] et al. presented a biosensor based on SPCE and improved the SPCE sensor for immunoassay based on two wavelengths. They detected simultaneously two antibodies with different labels [34]. The SPCE was used to perform the fluorescence immunoassay method in human samples such as human serum and human blood using anti-rabbit immunoglobulin G (IG) on the surface of metallic thin layer including gold or silver films [2]. Recently, graphene oxide (GO) was used to enhance the fluorescence signal in immunoassay based on fluorescence sensor. The GO was coated on the surface of metal thin layer and the SPCE signal enhanced about 20 times compared to SPCE without GO layer. The reverse Kretschmann configuration was used to measure the human IgG with sensitivity of about 0.006 ng/mL [49]. The SPCE is a versatile physical technique for investigating DNA and human gene. DNA hybridization was measured using SPCE that depends on interaction of fluorophore and surface plasmon. When DNA hybridization occurs, the angle of SPCE signal will be changed and it monitors the interaction of DNA with another DNA biomolecule [50]. Recently, the grating surface plasmon couple emission was considered as a highly sensitive analytical tools to recognize the biological molecules. The basic concept is the same as SPCE based on prism coupling. Figure 7 shows a grating SPCE structure that the grating was used to excited the surface plasmons at the interface of metal and dielectric medium [51]. Many researchers were focused on the application of the grating SPCE to recognize the biological molecule. [PERSON] et al. used the plasmonic grating to obtain the image single molecules [52]. They enhanced the emission intensity of fluorescence using surface plasmon resonance.