Unveiling Morphine: A Rapid and Selective Fluorescence Sensor for Forensic and Medical Analysis

Abstract

Opioid use, particularly morphine, is linked to CNS-related disorders, comorbidities, and premature death. Morphine, a widely abused opioid, poses a significant global health threat and serves as a key metabolite in various opioids. Here, we present a turn-off fluorescent sensor capable of detecting morphine with exceptional sensitivity and speed in various samples. The fluorescent sensor was developed through the dimerization process of 7-methoxy-1-tetralone and subsequent demethylation to produce the final product. Despite morphine possessing inherent fluorophoric properties and emitting light in an approximately similar wavelength as the sensor's fluorescent blue light, the introduction of the target molecule (morphine) in the presence of the sensor caused a reduction in the sensor's fluorescence intensity, which is attributable to the formation of the sensor-morphine complex. By utilizing this fluorescence quenching sensor, the chemo-selective detection of morphine becomes highly feasible, encompassing a linear range from 0.008 to 40 ppm with an impressive limit of detection of 8 ppb. Consequently, this molecular probe demonstrates a successful application in determining trace amounts of morphine within urine, yielding satisfactory analytical results. The study also explores the effect of several variables on the sensor's response and optimizes the detection of morphine in urine using a response surface methodology with a central composite design.

Keywords: CCD-RSM; forensic biological fluids; morphine; toxicology; turn-off sensor.

Figure 1

Synthesis process of 7,7′-Dimethoxy-1,1′-binaphthalene and 7′-Methoxy-[1,1′-binaphthalen]-7-ol.

Figure 2

Comparison between the FTIR spectra of 7-methoxy-1-tetralone, 7,7′-Dimethoxy-1,1′-binaphthalene, and 7′-Methoxy-[1,1′-binaphthalen]-7-ol.

Figure 3

Comparison between the Raman spectra of 7-methoxy-1-tetralone, 7,7′-Dimethoxy-1,1′-binaphthalene, and 7′-Methoxy-[1,1′-binaphthalen]-7-ol.

Figure 4

(a) The three-dimensional mapping graph illustrates how altering the excitation wavelength affects the intensity of the sensor’s emission peak. (b) The contour map displays the fluorescence emission and excitation spectra of the sensor, with the intersection denoting the position of the fluorescence peak (λ_ex = 325 nm, λ_em = 369 nm). (c) A comparison of the emission (λ_ex = 325 nm) and excitation (λ_em = 369 nm) spectra of 400 ppm 7′-Methoxy-[1,1′-binaphthalen]-7-ol dissolved in methanol. (d) The CIE chromaticity plot reveals the color coordinates of the emission beam, demonstrating that the molecule emits blue light upon excitation (λ_ex = 325 nm).

Figure 5

(a) The three-dimensional synchronous fluorescence spectroscopy mapping. (b) The influence of time on the fluorescence-emission intensity of the developed sensor.

Figure 6

(a) Compares the variations in the intensity of the fluorescence-emission peak due to alterations in the concentration of morphine, both in the presence and absence of the developed sensor. (b) Illustrates the sensor’s linear range, in response to morphine, displaying an R² value of 0.98 (λ_ex = 325 nm). (c) Demonstrates the linear range of morphine’s fluorescence peak in the absence of the sensor, accompanied by an R² value of 0.99 (λ_ex = 325 nm).

Figure 7

(a) Bar chart illustrating variations in sensor fluorescence when exposed to various drugs (20 ppm each) individually. F represents the fluorescence response of the sensor in the presence of the drug, while F’ signifies the sensor’s fluorescence response in the absence of any drugs. (b) The competition experiment on the effect of other drugs on morphine detection by developing a mixture of morphine (20 ppm) with other drugs (20 ppm each) separately. (c) The possible reaction sites for the formation of a non-fluorescent complex between morphine and the sensor. (d) Effect of temperature on fluorescence-emission intensity of the sensor in the presence of a constant amount of morphine (20 ppm in methanol).

Figure 8

Comparison of fluorescence-emission spectra. The graph illustrates the fluorescence-emission spectra of the sensor (100 ppm in methanol) in a 1:1 mixture with urine, morphine (40 ppm in methanol) in a 1:1 mixture with urine, pure methanol in a 1:1 mixture with urine, pure urine without any additives, and pure analytical-grade methanol.

Figure 9

(a) Sensor’s response to morphine concentration: This panel illustrates the dynamic response of the sensor as it detects variations in morphine concentration within urine samples. (b) Normal plot of residuals: In this plot, the residuals are visually examined for adherence to normal distribution assumptions, providing insights into the model’s performance. (c) Predicted-versus-actual graph: This graph showcases the predictive accuracy of the model by comparing the predicted sensor’s fluorescence emission with the actual values.

Figure 10

Three-dimensional plots of sensor’s fluorescence-emission response in urine samples: (a) interactive effect of morphine’s concentration and temperature; (b) interactive time and morphine’s concentration; (c) interactive effect of time and temperature; (d) interactive effect of sensor’s concentration and morphine’s concentration; (e) interactive effect of sensor’s concentration and temperature; (f) interactive effect of time and sensor’s concentration.

Figure 11

Two-dimensional desirability graphs versus actual points: (a) Actual factors include temperature at 18.53 °C and addition time at 7.47 min; (b) Actual factors include morphine’s concentration at 21.83 ppb and addition time at 7.47; (c) Actual factors include morphine’s concentration at 21.83 ppb and temperature at 18.53 °C (d) Actual factors include sensor’s concentration at 75 ppm and addition time at 7.47 min; (e) Actual factors include temperature at 18.53 °C and sensor’s concentration at 75 ppm; (f) Actual factors include morphine’s concentration at 21.83 ppb and sensor’s concentration at 75 ppm.