Light-induced Fluorescence Spectroscopy Research Articles

Early detection of stripe rust infection in wheat using light-induced fluorescence spectroscopy.

In the current study, the application of fluorescence spectroscopy along with the advanced statistical technique and confocal microscopy was investigated for the early detection of stripe rust infection in wheat grown under field conditions. The indigenously developed Fluorosensor fitted with LED, emitting monochromatic light was used that covered comparatively larger leaf area for recording fluorescence data thus presenting more reliable current status of the leaf. The examined leaf samples covered the entire range of stripe rust disease infection from no visible symptoms to the complete disease prevalence. The molecular changes were also assessed in the leaves as the disease progresses. The emission spectra mainly produce two fluorescence emission classes, namely the blue-green fluorescence (400-600nm range) and chlorophyll fluorescence (650-800nm range). The chlorophyll fluorescence region showed lower chlorophyll bands both at 685 and 735nm in the asymptomatic (early diseased) and symptomatic (diseased) leaf samples than the healthy ones as a result of partial deactivation of PSII reaction centers. The 735nm chlorophyll fluorescence band was either slight or completely absent in the leaf samples with lower to higher disease incidence and thus differentiate between the healthy and the infected leaf samples. The Hydroxycinnamic acids (caffeic and sinapic acids) showed decreasing trend, whereas the ferulic acid increased with the rise in disease infection. Peak broadening/shifting has been observed in case of ferulic acid and carotenes/carotenoids, with the increase in the disease intensity. While using the LEDs (365nm), the peak broadening and the decline in the chlorophyll fluorescence bands could be used for the early prediction of stripe rust disease in wheat crop. The PLSR statistical techniques discriminated well between the healthy and the diseased samples, thus showed promise in early disease detection. Confocal microscopy confirmed the early prevalence of stripe rust disease infection in a susceptible variety at a stage when the disease is not detectable visually. It is inferred that fluorescence emission spectroscopy along with the chemometrics aided in the effective and timely diagnosis of plant diseases and the detected signatures provide the basis for remote sensing.

In-line Fluorescence Spectroscopy for Quantification of Low Amount of Active Pharmaceutical Ingredient

The pharmaceutical industry is currently implementing new manufacturing principles and modernizing the related processing solutions. A key element in this development is implementation of process analytical technologies (PAT) for measuring product quality in a real-time mode, ideally for a continuously operating processing line. Near-infrared (NIR) spectroscopy is widely used for this purpose, but has limited use for low concentration formulations, due to its inherent detection limit. Light-induced fluorescence (LIF) spectroscopy is a PAT tool that can be used to quantify low concentrations of active pharmaceutical ingredient, and recent development of instrumentation has made it available for in-line applications. In this study, the content of tryptophan in a dynamic powder flow could be measured as low as 0.10 w/w % with LIF spectroscopy with good accuracy of RMSEP = 0.008 w/w %. Both partial least squares regression and support vector machines (SVM) were investigated, but we found SVM to be the better option due to non-linearities between the calibration test and the in-line measurements. With the use of SVM, LIF spectroscopy is a promising candidate for low concentration applications where NIR is not suitable.

Feasibility of Using Light-Induced Fluorescence Spectroscopy for Low-Dose Formulations Monitoring and Control

Light-induced fluorescence was evaluated as a process analytical tool in the development of quantitative models for the monitoring of a low-dose formulation manufacturing process. The system, equipped with a probe, was positioned in a tablet press feed-frame to monitor the active pharmaceutical ingredient content of the flowing powder before compression. Modeling errors of 1.1% and lower in cross-validation for a 0.67% w/w drug load were observed, which is remarkable for a process analytical tool. While light-induced fluorescence is emerging as a promising technology, robustness improvements and demonstration of method validation are still required. The technology is expected to become a tool of choice, ready for manufacturing deployment, to support the monitoring and potentially control of low-dose pharmaceutical formulations.

Using multiple Process Analytical Technology probes to monitor multivitamin blends in a tableting feed frame

As Process Analytical Technology (PAT) implementation grows in the pharmaceutical industry, more studies are being performed to evaluate its suitability in new applications and processes within the manufacturing chain. As the last step in tablet production, the compression stage represents a critical phase that ensures product quality. In-line control put in place at this stage has the potential to detect powder blends that are out of specification limits and, thus, help to improve product quality.The objectives of the present project are to quantify the composition of a commercial 31-component multivitamin powder blend in real time on an industrial feed frame, using 3 different PAT tools: light-induced fluorescence spectroscopy, near infrared spectroscopy and red, green and blue color imaging.To do so, the concentrations of 5 components (Beta-Carotene, Riboflavin, Ferrous Fumarate, Ginseng and Ascorbic Acid) were alternately changed and monitored with one or many probes. Transition periods between batches served to quantify different powder flow dynamics with sequential composition step changes.The results showed that 4 out of 5 components, each present in commercially-relevant concentrations, could be monitored by one or more tools. Flow dynamics were measured and found to vary significantly in different powder blends.

Monitoring the concentration of flowing pharmaceutical powders in a tableting feed frame

The use of process analytical technology (PAT) tools is increasing steadily in the pharmaceutical industry. Such tools are now located throughout the process. When producing tablets, the tableting step itself may be the ideal moment to assess final product composition. Being the last unit operation in tablet production where the elements are still free flowing, it is relatively straightforward to ascertain the composition of the blend in real time. However, a single probe cannot be expected to monitor the composition of every component of a multicomponent blend. In this study, three PAT tools (light-induced fluorescence spectroscopy, near-infrared spectroscopy and color (RGB) imaging) simultaneously checked the composition of powder blends flowing through the feeding unit (feed frame) of a tablet press. The results demonstrate the potential of these tools in monitoring changes in the concentration of a multicomponent mixture in real time, providing users with means to both scrutinize the process and better understand phenomena occurring inside the feed frame.

Bringing Light into the Diagnosis of Skin Disorders - Short Review on Laser Induced Fluorescence Spectroscopy and Optical Coherence Tomography in Dermatology

The study of optospectral techniques for the non-invasive, in vivo diagnosis of skin diseases has intensified in the last years. Optical diagnosis methods have already started to prove their ability to reveal specific skin functions and to identify skin lesions and their various stages, allowing for the early diagnosis of skin diseases and monitoring of their treatments. At the moment, these techniques have great inter and intra-patient variations, which could be overcome by the use of combined optical techniques, assuring greater accuracy and complementary information, and thus, entering the mainstream of medical practice. After a brief review concerning light-induced fluorescence spectroscopy (LIFS) and optical coherence tomography (OCT) methods, the article intends to present the benefits of applying a combination of both methods for improved diagnostic accuracy in the case of both benign and malignant disorders of the skin. Keywords: Combined optical techniques, fluorescence spectroscopy, melanoma, fluorophores, optical coherence tomography, skin diseases.

Development of a multivariate light-induced fluorescence (LIF) PAT tool for in-line quantitative analysis of pharmaceutical granules in a V-blender

Process analytical technologies (PAT) enable process insight, process control and real-time testing. Light-induced fluorescence (LIF) spectroscopy is especially well suited for low-concentration ingredients as, in many cases, it is the most sensitive probe of the in-line PAT toolbox. This study is aimed at verifying the applicability of a multivariate LIF analyzer to monitor granulated powder blends in industrial settings. Its targets are to: (1) evaluate the critical parameters of powders to obtain robust, precise and accurate concentration predictions and (2) assess technology performance for in-line monitoring of blending operations. Varying dye properties, moisture levels and particle sizes have been shown to have the most significant impact on fluorescence emission. Reliable quantitative models can be obtained by controlling and/or mitigating these factors.

Measurement of XeI and XeII velocity in the near exit plane of a low-power Hall effect thruster by light induced fluorescence spectroscopy

Near exit plane non-resonant light induced fluorescence spectroscopy is performed in a Hall effect low-power Xenon thruster at discharge voltage of 250 V and anode flow rate of 0.7 mg/s. Measurements of the axial and radial velocity components are performed, exciting the 6s(2)[3/2]2(o)→6p(2)[3/2]2 transition at 823.16 nm in XeI and the 5d[4]7/2→6p[3]5/2(o) transition at 834.724 nm in XeII. No significant deviation from the thermal velocity is observed for XeI. Two most probable ion velocities are registered at a given position with respect to the thruster axis, which are mainly attributed to different areas of creation of ions inside the acceleration channel. The spatial resolution of the set-up is limited by the laser beam size (radius of the order of 0.5 mm) and the fluorescence collection optics, which have a view spot diameter of 8 mm.

LIGHT-INDUCED FLUORESCENCE SPECTROSCOPY AND OPTICAL COHERENCE TOMOGRAPHY OF BASAL CELL CARCINOMA

Many up-to-date optical techniques have been developed and applied recently in clinical practice for obtaining qualitatively and quantitatively new data from the investigated lesions. Due to their high sensitivity in detection of small changes, these techniques are widely used for detection of early changes in biological tissues. Light-induced fluorescence spectroscopy (LIFS) is one of the most promising techniques for early detection of cutaneous neoplasia. Increasing number of recent publications have suggested that optical coherence tomography (OCT) also has potential for non-invasive diagnosis of skin cancer. This recent work is a part of clinical trial procedure for introduction of LIFS technique into the common medical practice in National Oncological Medical Center in Bulgaria for diagnosis of non-melanoma skin cancer. We focus our attention here on basal cell carcinoma lesions and their specific features revealed by LIFS and OCT analysis. In this paper we prove the efficiency of using the combined LIFS-OCT method in skin lesions studies by integrating the complimentary qualities of each particular technique. For LIFS measurements several excitation sources, each emitting at 365, 385 and 405 nm maxima are applied. An associated microspectrometer detects in vivo the fluorescence signals from human skin. The main spectral features of the lesions and normal skin are discussed and their possible origins are indicated. OCT images are used to evaluate the lesion thickness, structure and severity stage, when possible. The obtained results could be used to develop a more complete picture of optical properties of these widely spread skin disorders. At the same time, our studies show that the combined LIFS-OCT method could be introduced in clinical algorithms for early tumor detection and differentiation between normal/benign/malignant skin lesions.

Early detection of premalignant changes in cell cultures using light-induced fluorescence spectroscopy

Light-induced fluorescence (LIF) spectroscopy has demonstrated ability as a novel, noninvasive and sensitive technology for early detection of cancer. The goal of the present study is to examine the potential of this spectroscopic method for early detection and characterization of premalignant changes. As a model we used both cell lines and primary cells, which were transformed to malignant by retrovirus. Fluorescence measurements and morphological observations of the infected cells were performed at various postinfection times. Our results showed gradual attenuation of fluorescence intensities due to cancer progression which corresponds to aromatic amino acids and nicotinamide adenine dinucleotide (NADH) molecules. In order to obtain grading and supervised classifications of the spectral premalignant changes we used approaches of linear discriminant analysis. The classifications based on Mahalanobis distances allowed us to demonstrate that the accuracy of identification of premalignant stages varied between 83.1% and 96.4%. In summary, we conclude that LIF in tandem with proper statistical tools may be a promising technique for early detection of malignant progression.

The Influence of Drying on Quantitative Laser Fluorescence and Optical Pathlengths in Incipient Natural Caries Lesions

Drying effects in 14 natural lesions were studied with quantitative light-induced fluorescence and optical pathlength spectroscopy. Results were compared with clinical judgments of the lesion surface and microradiographical characterizations of the lesions. Relative fluorescence and average pathlength decreased as a function of drying time with a decay time ranging from 35.5 to <1 min. Depth and mineral loss correlated with average pathlength total changes (r = –0.79/–0.60, respectively) and poorly with total fluorescence changes (r 0.3). The decay time of the drying process for the relative fluorescence correlated well with a theoretical model based on water diffusion in lesion and surface layer, but only for large decay times. Clinical judgments could not be related to the surface layer properties or the changes in the average pathlength, but were weakly related to the changes in the relative fluorescence. We conclude that (i) fluorescence effects are mostly due to the screening by the lesion of the fluorescence from the dentin and enamel-dentin junction; (ii) water evaporation in lesions conforms to the diffusion laws only in large lesions with low surface layer penetrability; (iii) the evaporation process is controlled by the surface layer only for small surface penetrabilities (≈ 0.1 vol% µm^–1).

Endoscopic fluorescence spectroscopy in the upper GI tract for the detection of GI cancer: initial experience

OBJECTIVE: The aim of this study was to investigate autofluorescence spectroscopy using violet-blue excitation light for the in vivo diagnosis of GI cancer during routine endoscopy. METHODS: Fluorescence spectra were obtained from normal mucosa and cancerous lesions of the esophagus and stomach. The spectroscopic system used comprised a special light source capable of delivering either white or violet-blue light to induce autofluorescence of tissue via the endoscope. Endogenous fluorescence spectra emitted by the tissue were recorded with a fiberoptic probe and analyzed with a spectrographic detector system consisting of a polychromator with a photodiode array and an optical multichannel analyzer. The data of each spectrum were sampled within the range of 450–700 nm and stored in a personal computer. RESULTS: Esophageal squamous cell cancer, adenocarcinoma of the esophagus, and adenocarcinoma of the stomach show specific differences in the emitted fluorescence spectra compared with normal mucosa. CONCLUSIONS: Light-induced fluorescence spectroscopy might be a useful tool for the endoscopic in vivo detection of dysplasia and early carcinoma in the upper GI tract. Further trials are needed to test the validity of this new optical detection system.

Light-induced autofluorescence spectroscopy for the endoscopic detection of esophageal cancer

Background: Any innovative optical system that facilitates the early endoscopic detection of neoplastic change in the GI mucosa has the potential to greatly improve survival and quality of life for patients prone to have GI malignancies develop. The present article describes light-induced autofluorescence spectroscopy with violet-blue excitation light for in vivo diagnosis of cancerous tissue of the esophagus during routine endoscopy. Methods: One hundred twenty-nine endogenous fluorescence spectra were obtained from normal mucosa and malignant lesions in 9 patients with squamous cell cancer and 4 with adenocarcinoma of the esophagus. Following spectrographic measurements, biopsy specimens were obtained for definitive classification of the spectra. A special light source capable of delivering either white or violet-blue light for excitation of tissue autofluorescence by means of an endoscope was used. Endogenous fluorescence spectra emitted by tissues were detected with a fiberoptic probe and analyzed with a spectrograph. Results: Squamous cell cancer and adenocarcinoma of the esophagus exhibit specific changes in the emitted fluorescence spectra as compared with normal mucosa. Based on the results obtained in earlier studies, malignant and benign spectra were differentiated with the aid of a mathematical algorithm. By using this algorithm, a sensitivity of 97% and specificity of 95% were obtained for the diagnosis of esophageal carcinoma. Conclusions: Light-induced fluorescence spectroscopy is useful for the endoscopic detection of squamous cell cancer and adenocarcinoma of the esophagus. This spectroscopic study provides a basis for the design of a simplified autofluorescence imaging system for detection of esophageal neoplasms. (Gastrointest Endosc 2001;54:195-201.)

Pharmacokinetics and pharmacodynamics of tetra( m-hydroxyphenyl)chlorin in the hamster cheek pouch tumor model: comparison with clinical measurements

The pharmacokinetics (PK) of the photosensitizer tetra( m-hydroxyphenyl)chlorin (mTHPC) was measured by optical fiber-based light-induced fluorescence spectroscopy (LIFS) in the normal and tumoral cheek pouch mucosa of 29 Golden Syrian hamsters with chemically induced squamous cell carcinoma. Similar measurements were carried out on the normal oral cavity mucosa of five patients up to 30 days after injection. The drug doses were between 0.15 and 0.3 mg per kg of body weight (mg/kg), and the mTHPC fluorescence in the tissue was excited at 420 nm. The PK in both human and hamster exhibited similar behavior although the PK in the hamster mucosa was slightly delayed in comparison with that of its human counterpart. The mTHPC fluorescence signal of the hamster mucosa was smaller than that of the human mucosa by a factor of about 3 for the same injected drug dose. A linear correlation was found between the fluorescence signal and the mTHPC dose in the range from 0.075 to 0.5 mg/kg at times between 8 and 96 h after injection. No significant selectivity in mTHPC fluorescence between the tumoral and normal mucosa of the hamsters was found at any of the applied conditions. The sensitivity of the normal and tumoral hamster cheek pouch mucosa to mTHPC photodynamic therapy as a function of the light dose was determined by light irradiation at 650 nm and 150 mW/cm 2, 4 days after the injection of a drug dose of 0.15 mg/kg. These results were compared with irradiations of the normal oral and normal and tumoral bronchial mucosa of 37 patients under the same conditions. The reaction to PDT of both types of human mucosae was considerably stronger than that of the hamster cheek pouch mucosa. The sensitivity to PDT became comparable between hamster and human mucosa when the drug dose for the hamster was increased to 0.5 mg/kg. A significant therapeutic selectivity between the normal and neoplastic hamster cheek pouch was observed. Less selectivity was found following irradiations of normal mucosa and early carcinomas in the human bronchi. The pharmacodynamic behavior of mTHPC was determined by test irradiations of the normal mucosa of hamsters and patients between 6 h and 8 days after injection of 0.5 and 0.15 mg/kg in the hamsters and the patients, respectively. The normal hamster cheek pouch showed a maximum response to irradiation 6 h after injection and then decreased continuously to no observable reaction at 8 days after injection. The reaction of the normal human oral mucosa, however, showed an increasing sensitivity to the applied light between 6 h and 4 days after mTHPC injection and then decreased again at 8 days. The hamster model with the chemically induced early squamous cell cancer in the cheek pouch thus showed some similarity to the early squamous cell cancer of the human oral mucosa considering the PK. However, a quantitative difference in fluorescence signal for identical mTHPC doses as well as a significant difference in pharmacodynamic behavior were also observed. The suitability of this animal model for the optimization of PDT parameters in the clinic is therefore limited. Hence great care must be taken in screening new dyes for PDT of early squamous cell cancer of the upper aerodigestive tract based upon observables in the hamster cheek pouch model.

Rapid Communication: Stability of the Fluorescence Measurement of Foscan® in the Normal Human Oral Cavity as an Indicator of its Content in Early Cancers of the Esophagus and the Bronchi

Photodynamic therapy (PDT) with Foscan (mTHPC) is used to cure early cancers of the esophagus or the tracheobronchial tree. However, fixed PDT parameters (drug dose, light dose, etc.) do not permit an accurate prediction of the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjusted to the drug dose shortly before the PDT. This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measurement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed. The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applied to the probe. These measurements prove to be not only correlated to similar measurements in the esophagus or the bronchi but also more consistent and less sensitive to the location and the applied pressure. The buccal mucosa is therefore recommended as a test site for measuring the Foscan fluorescence signal at the time of PDT in the esophagus or the bronchi. This measurement is accurate enough for use in light-dose adjustment.

Stability of the Fluorescence Measurement of Foscan® in the Normal Human Oral Cavity as an Indicator of its Content in Early Cancers of the Esophagus and the Bronchi

Photodynamic therapy (PDT) with Foscan (mTHPC) is used to cure early cancers of the esophagus or the tracheobronchial tree. However, fixed PDT parameters (drug dose, light dose, etc.) do not permit an accurate prediction of the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjusted to the drug dose shortly before the PDT. This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measurement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed. The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applied to the probe. These measurements prove to be not only correlated to similar measurements in the esophagus or the bronchi but also more consistent and less sensitive to the location and the applied pressure. The buccal mucosa is therefore recommended as a test site for measuring the Foscan fluorescence signal at the time of PDT in the esophagus or the bronchi. This measurement is accurate enough for use in light-dose adjustment.

Autofluorescence in normal and malignant human oral tissues and in DMBA-induced hamster buccal pouch carcinogenesis.

Light-induced fluorescence spectroscopy was conducted on human oral malignant and normal tissues. Under 330-nm excitation wavelength, significant differences in fluorescence intensity were observed around 380- and 460-nm emission. Furthermore, 7,12-dimethylbenz[a]anthracene (DMBA)-induced carcinogenesis in hamster buccal pouch was investigated to elucidate whether similar alterations of fluorescence spectroscopy occurred during the development of squamous cell carcinoma. Similar to the spectral profiles of human oral malignant and normal tissues, the most intense fluorescence peaks in the pouches occurred at 380 nm and 460 nm emission under 330 nm excitation wavelength. At 380 nm emission, the fluorescence intensity of normal pouch mucosa was stronger than those of DMBA-treated abnormal tissues at different stages of carcinogenesis. However, at 460 nm emission, the fluorescence intensity of DMBA-treated tissues was not only stronger than that of normal pouch mucosa but also shifted to 470 nm. These results suggest that under 330 nm excitation wavelength fluorescence spectroscopy may be useful for the detection of oral malignant lesions.

Clinical Evaluation of the Cutaneous Phototoxicity of 5,10,15,20‐Tetra (m‐hydroxyphenyl)chlorin

The cutaneous phototoxic reaction induced by intravenous injection of 5,-10,-15,-20-tetra(m-hydroxyphenyl)chlorin (mTHPC) has been clinically evaluated in patients undergoing photodynamic therapy. These tests were performed on the backs of 23 patients with a solar simulator at various times after drug administration ranging from 5 h to 57 days. The mTHPC doses ranged from 0.1 to 0.3 mg/kg, and the illuminations lasted from 30 s up to 8 min. These tests have shown that the duration of the skin photosensitization induced after a typical therapeutic dose of mTHPC (0.15 mg/kg) is less important than with Photofrin (2 mg/kg). The level of mTHPC in the skin was also assessed in vivo and at times corresponding to the irradiations using an optical fiber-based spectrofluorometer. This study indicates that the light-induced fluorescence spectroscopy of mTHPC enables prediction of the degree of photosensitivity of the skin.

Pharmacokinetics of Tetra (m‐hydroxyphenyl)chlorin in Human Plasma and Individualized Light Dosimetry in Photodynamic Therapy

The pharmacokinetics of the photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC) was investigated in the plasma of 20 patients by absorption and fluorescence spectroscopy. The temporal behavior was characterized by a rapid decrease in concentration during the first minutes after intravenous injection of 0.15 mg/kg mTHPC. A minimum concentration in the plasma was reached after about 45 min. The drug concentration then increased again, attaining a maximum after about 10 h, after which it decreased again with a halflife of about 30 h. Irradiation tests in the oral cavity at different time intervals after the injection revealed that the tissue reaction was only partially correlated with the mTHPC plasma level. The tissue response was stronger at later drug-light intervals (1-4 days) than during the first hours after injection even though the mTHPC plasma concentration was higher at the shorter times. Relative mTHPC concentrations were also measured in the mucosae of the oral cavity, the esophagus and the bronchi of 27 patients by light-induced fluorescence spectroscopy using an optical fiber-based spectrometer. These measurements were performed prior to photodynamic therapy (PDT), 4 days after injection of the photosensitizer. Highly significant linear correlations were found between the relative mTHPC concentrations in the mucosae of these three organs. Likewise, the plasma levels of mTHPC measured just before PDT were significantly correlated with the mTHPC concentrations in the three types of mucosae mentioned above. These results indicate that mTHPC plasma levels measured just before PDT can be used for PDT light dosimetry.

Fluorescence spectroscopic identification of 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis.

An attempt was made to study whether light-induced fluorescence spectroscopy could be exploited to discriminate premalignant and malignant tissues of hamster buccal pouch carcinogenesis from normal tissues during a 16 week regimen of tri-weekly topical application of 7,12-dimethylbenz[a]anthracene (DMBA) in liquid paraffin. Histologically, the DMBA-treated buccal mucosa showed hyperplastic changes at 4-6 weeks, papillomas at 8-10 weeks, early invasive carcinomas at 11-13 weeks and finally well-differentiated squamous cell carcinomas at 14-16 weeks of treatment. Acetone extracts of these different staged tissues with age matched control tissues were excited at 405 and 420 nm and the emissions were scanned from 430 and 440 to 700 nm respectively. The spectral profiles of control and transformed tissues were found to be different, each displaying their own characteristic prominent maxima and other spectral marks. The spectra of transformed tissues showed characteristic peaks around 620-630 nm which did not appear in control tissues and the fluorescent intensities at 630 nm [FI(630)nm] were significantly increased from early stages onwards when compared to controls. The spectra of DMBA carcinomas developed at the 18th week after withdrawal of DMBA application at the 10th week and carcinoma extract spiked with DMBA confirmed the peak around 620-630 could be attributed only to porphyrin compounds accumulated in transformed tissues. Furthermore, the ratios of FI(520)nm/FI(630)nm of transformed tissues were also significantly decreased when compared to control tissues. This diagnostic test had a very close resemblance with respect to histological studies. These results suggest that this technique using conventional light-induced fluorescence spectroscopy may be useful for early diagnosis of premalignant and malignant lesions of oral cavity.