تجزیه و تحلیل حساسیت فرکانس سیستم مدار فرکانس آشکار ساز نور سری با استفاده از پارامترهای مدار کریستال کوارتز

The 48 MHz series photodetector frequency circuit systems matched with different quartz crystals were developed for frequency sensitivity analysis. In accordance with derived theory of series photodetector frequency circuit system, the circuit parameters of quartz crystal such as Rq and Cq can be applied to improve the frequency sensitivity. On the basis of parameter adjustment, the quartz crystal with proper Rq and Cq was selected to improve the frequency sensitivity of fluorescence detection. In the optimal conditions of Rq and Cq, the detection limit of U1392-Hex fluorescence dye concentration 3.3 pmol/L can be measured by 48 MHz sensor system. Moreover, the frequency method showed that the detection limit of U1392-Hex fluorescence dye concentration was lower than the conventional fluorescence technique by 2–3 orders. The result also indicated that the frequency shift ΔF was linearly related to the logarithm of fluorescence dye concentration in the range 3.3 pmol/L–3.3 μmol/L.

On the basis of fluorescence detection theorem [1] and [2], the series photodetector frequency circuit system has been proposed for detection of fluorescence dye concentration. While emissive fluorescence irradiated on the photodetector, the photocurrent of photodetector was produced to influence the frequency response of series photodetector frequency circuit system. The detection system can transduce the fluorescence signal to frequency response for detection of fluorescence dye concentration. The previous study presented that frequency response can be influenced during emissive fluorescence irradiating on the photodetector of series photodetector frequency circuit system. The fluorescence dye concentration can be appropriately estimated by the frequency shift. In accordance with the fluorescence detection experiment of 100 MHz sensor system, the detection limit of U1392-HEX fluorescence dye concentration 3.3 pmol/L can be measured. Although the 100 MHz sensor system has higher frequency sensitivity for fluorescence detection, the 100 MHz quartz crystal with stable frequency response cannot be manufactured easily. Therefore, the lower resonance frequency of series photodetector frequency circuit system which has high frequency sensitivity was developed and analyzed. From previous study, the frequency shift of 48 MHz series photodetector frequency circuit system matched with photodetector APT, PDMS focusing lens of diameter 10 mm, and supply voltage 5.8 V increased linearly from 3.3 pmol/L to 333.3 nmol/L [3]. The result had the same detection limit of fluorescence dye concentration as 100 MHz sensor system. It meant that the 48 MHz sensor system with effect of PDMS focusing lens and enhanced bias of photodetector had higher frequency sensitivity to detect lower fluorescence dye concentration. Based on 48 MHz series photodetector frequency circuit system matched with proper circuit parameter of quartz crystal, the improvement method of frequency sensitivity was proposed in this research. According to the theory analysis of frequency sensitivity, the circuit parameters such as Rq and Cq were discussed in the improvement experiment of frequency sensitivity. The 48 MHz sensor system was utilized to analyze the fluorescence detection characteristics and to evaluate the practicability of DNA hybridization with fluorescence label. The frequency method was also compared with conventional fluorescence techniques in terms of detection limit of fluorescence dye concentration.

The fluorescence detection system with green laser source was set up for Hex fluorescence sample detection. In this research of frequency sensitivity, we had found that the circuit parameters of quartz crystals were the important factors for frequency sensitivity improvement of series photodetector frequency circuit system. The detection limit of U1392-Hex fluorescence dye concentration 3.3 pmol/L can be measured by 48 MHz sensor system matched with quartz crystal IQC. The results also showed that the proposed method had the same detection limit of fluorescence dye concentration as 100 MHz sensor system. It can be concluded that the 48 MHz sensor system can be utilized for quantitative analysis of fluorescence dye concentration by frequency shift. The fluorescence experiments also showed that 48 MHz sensor system had a potential application in the detection of DNA hybridization with fluorescence label.