## 4 Results and Discussions
### Excitation/Fluorescence Spectrum Matrix
These maximum and minimum values of the fluorescence ratios were then used as identifying characteristics of each species. For each species, an identifier was calculated (GAD, GAL, SUE and TAM on Equation (2)). Maximum ratios from Table 6 are in the numerator and minimum ratios in the denominator of equations to calculate GAD, GAL, SUE and TAM (Equation (2)), but other ratios were also added to improve selectivity. A coefficient was also used to normalize all identifiers to a maximum value of 1 (1/284.6, 1/0.24, 61.8 and 1/20,423 respectively). \[ \begin{array}{l}GAD\ =\ \frac{F_{\text{F}X/\text{C}X}\times F_{\text{F}X/ \text{D}X}\times F_{\text{C}X/\text{D}X}\times F_{\text{F}X/\text{F}X/\text{F}X }}{284.6},\\ \\ GAL\ =\ \frac{F_{\text{C}X/\text{C}X}\times F_{\text{F}X/\text{D}X}\times F_{ \text{F}X/\text{D}X}\times F_{\text{F}X/\text{D}X}\times F_{\text{D}X/\text{F} X/\text{D}X}}{284.6},\\ \\ SUE\ =\ \frac{F_{\text{C}X/\text{C}X}\times F_{\text{C}X/\text{A}X}\times F_{ \text{D}X/\text{A}X}\times F_{\text{F}X/\text{F}X/\text{F}X/\text{C}X}\times F _{\text{D}X/\text{D}Y}},\\ \\ TAM\ =\ \frac{F_{\text{F}X/\text{A}X}\times F_{\text{C}X/\text{A}X}\times F_{ \text{D}X/\text{A}X}\times F_{\text{F}X/\text{F}X/\text{F}X}\times F_{\text{C }X/\text{D}X}}{284.6},\\ \\ \end{array}  \tag{2}\]  
Validation of the equations was made by calculating the four identifiers (Equation (2)) with the fluorescence values of the four species (Table 6), resulting in the values in Table 7.  
The species _Nannochloropsis gaditana_ and _Isochrysis galbana_ are clearly identified from the calculated identifier GAD and GAL, respectively. The identifier GAD showed the highest value (1.00) when _Nannochloropsis gaditana_ is present, whereas this identifier has low values (0.24, 0.21 and 0.00) when calculated with the fluorescence measurements of the three other species. The identifier GAL has the highest value (1.00) with the fluorescence of _Isochrysis Galbana_, but very small values (0.08, 0.09 and 0.01) when calculated from the fluorescence measurements corresponding to the three other species. In addition, the species _Tetraselmis suceica_ can be identified, but with less confidence than the previous species. The identifier SUE has the value 1.00 when calculated with the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Ratio**} & \multicolumn{5}{c}{**Specie**} \\ \cline{2-5}  & _Nannochloropsis_ & _Isochrysis_ & _Tetraselmis_ & _Alexandrium_ \\  & _gaditana_ & _galbana_ & _sucecia_ & _tamarense_ \\ \hline F\({}_{\text{B}X}\)/\({}_{\text{C}X}\) & 1.41 (M) & 0.80 (m) & 1.02 & 0.83 \\ F\({}_{\text{B}X}\)/\({}_{\text{D}X}\) & 3.98 (M) & 1.44 & 2.65 & 1.17 (m) \\ F\({}_{\text{B}X}\)/  
fluorescence of species _Tetraselmis suecia_, and values bellow 0.48 when calculated with the fluorescence measurements from the other species. The toxic species (_Alexandrium Tamarense_) can be clearly identified from _Nannochloropsis gaditana_ and _Tetraselmis suecia_. However, TAM showed a value of 0.54 in the presence of _Isochrysis galhana_, a value that still allows its identification, but with less confidence. An identifying algorithm should calculate the value of the four identifiers (GAL, GAD, SUE and TAM), and the higher value obtained in these four identifiers reveals the presented species. If more different species are presented for identification, the same methodology can be used. However, more emission ratios (than the ones presented in Table 6) should be used in order to improve selectivity of the identification process. We were, therefore, able to identify phytoplankton taxonomic groups using a commercial fluorimeter, thus allowing to fulfil the objective of this work: to develop a lab-on-a-chip sensor capable of distinguishing toxic and non-toxic phytoplankton species through the analysis of fluorescence spectrum and intensity at several excitation wavelengths.