Singlet oxygen luminescence as an in vivo photodynamic therapy dose metric: validation in normal mouse skin with topical amino-levulinic acid

Two-dimensional singlet oxygen imaging with its near-infrared luminescence during photosensitization

Photodynamic therapy is a promising cancer treatment that involves activation of photosensitizer by visible light to create singlet oxygen. This highly reactive oxygen species is believed to induce cell death and tissue destruction in PDT. Our approach used a near-infrared area CCD with high quantum efficiency to detect singlet oxygen by its 1270-nm luminescence. Two-dimensional singlet oxygen images with its near-infrared luminescence during photosensitization could be obtained with a CCD integration time of 1 s, without scanning. Thus this system can produce singlet oxygen luminescence images faster and achieve more accurate measurements in comparison to raster-scanning methods. The experimental data show a linear relationship between the singlet oxygen luminescence intensity and sample concentration. This method provides a detection sensitivity of 0.0181 μg∕ml (benzoporphyrin derivative monoacid ring A dissolved in ethanol) and a spatial resolution better than 50 μm. A pilot study was conducted on a total of six female Kunming mice. The results from this study demonstrate the system's potential for in vivo measurements. Further experiments were carried out on two tumor-bearing nude mice. Singlet oxygen luminescence images were acquired from the tumor-bearing nude mouse with intravenous injection of BPD-MA, and the experimental results showed real-time singlet oxygen signal depletion as a function of the light exposure.

Photodynamic therapy as consolidation treatment for primary cutaneous adenoid cystic carcinoma: a case report

OBJECTIVE

The purpose of this case report was to evaluate the efficacy of photodynamic therapy (PDT) for a patient with primary cutaneous adenoid cystic carcinoma (PCACC).

MATERIALS AND METHODS

A 53-year-old female patient presented with a lesion at the pre-auricular area. After performing a local resection along a margin of 0.5 cm beyond the surrounding tissue, PCACC was clearly revealed based on the histological features and the exclusion of differentiation of other metastasis in the skin. The patient was then treated repetitively with 5-aminolevulinic acid (ALA)-PDT. After the final PDT treatment, the control pathological biopsy at the same location demonstrated no tumor cell in the specimen.

RESULTS

The 40-month follow-up diagnosis showed no evidence of recurrence or metastasis observed on the treated area.

CONCLUSION

ALA-PDT was a safe and effective therapy for obtaining good cosmetic results and reducing recurrence in this case report.

Nanoscintillator conjugates as photodynamic therapy-based radiosensitizers: calculation of required physical parameters

The recent demonstration of nanoscale scintillators has led to interest in the combination of radiation and photodynamic therapy. In this model, scintillating nanoparticles conjugated to photosensitizers and molecular targeting agents would enhance the targeting and improve the efficacy of radiotherapy and extend the application of photodynamic therapy to deeply seated tumors. In this study, we calculated the physical parameters required for these nanoparticle conjugates to deliver cytotoxic levels of singlet oxygen at therapeutic radiation doses, drawing on the published literature from several disparate fields. Although uncertainties remain, it appears that the light yield of the nanoscintillators, the efficiency of energy transfer to the photosensitizers, and the cellular uptake of the nanoparticles all need to be fairly well optimized to observe a cytotoxic effect. Even so, the efficacy of the combination therapy will likely be restricted to X-ray energies below 300 keV, which limits the application to brachytherapy.

Pulsed diode laser-based singlet oxygen monitor for photodynamic therapy: in vivo studies of tumor-laden rats

Photodynamic therapy (PDT) is a promising cancer treatment that involves optical excitation of photosensitizers that promote oxygen molecules to the metastable O(2)(a(1)Delta) state (singlet oxygen). This species is believed to be responsible for the destruction of cancerous cells during PDT. We describe a fiber optic-coupled, pulsed diode laser-based diagnostic for singlet oxygen. We use both temporal and spectral filtering to enhance the detection of the weak O(2)(a-->X) emission near 1.27 microm. We present data that demonstrate real-time singlet oxygen production in tumor-laden rats with chlorin e6 and 5-aminolevulinic acid-induced protoporphyrin photosensitizers. We also observe a positive correlation between post-PDT treatment regression of the tumors and the relative amount of singlet oxygen measured. These results are promising for the development of the sensor as a real-time dosimeter for PDT.

In-vivo singlet oxygen dosimetry of clinical 5-aminolevulinic acid photodynamic therapy

Photodynamic therapy (PDT) is a viable treatment option for a wide range of applications, including oncology, dermatology, and ophthalmology. Singlet oxygen is believed to play a key role in the efficacy of PDT, and on-line monitoring of singlet oxygen during PDT could provide a methodology to establish and customize the treatment dose clinically. This work is the first report of monitoring singlet oxygen luminescence in vivo in human subjects during PDT, demonstrating the correlation of singlet oxygen levels during PDT with the post-PDT photobiological response.

The physics, biophysics and technology of photodynamic therapy

Photodynamic therapy (PDT) uses light-activated drugs to treat diseases ranging from cancer to age-related macular degeneration and antibiotic-resistant infections. This paper reviews the current status of PDT with an emphasis on the contributions of physics, biophysics and technology, and the challenges remaining in the optimization and adoption of this treatment modality. A theme of the review is the complexity of PDT dosimetry due to the dynamic nature of the three essential components -- light, photosensitizer and oxygen. Considerable progress has been made in understanding the problem and in developing instruments to measure all three, so that optimization of individual PDT treatments is becoming a feasible target. The final section of the review introduces some new frontiers of research including low dose rate (metronomic) PDT, two-photon PDT, activatable PDT molecular beacons and nanoparticle-based PDT.

Cancer in patients with ulcerative colitis, Crohn's disease and coeliac disease: record linkage study

OBJECTIVE

The objective of this study was to determine the risk of cancers in cohorts of patients with ulcerative colitis, Crohn's disease, or coeliac disease, compared with the risk in a control cohort.

METHOD

The method used was the analysis of a linked statistical database of hospital and mortality data in an area in southern England.

RESULTS

Rate ratios for cancer (excluding cases occurring within the first year of follow-up), compared with the value of 1 in the control cohort, were 1.25 [95% confidence interval (CI), 1.13-1.39] in patients with ulcerative colitis, 1.27 (95% CI, 1.11-1.45) with Crohn's disease, and 1.16 (95% CI, 0.94-1.43) with coeliac disease. In patients with ulcerative colitis or Crohn's disease, there was a significantly high risk of cancer of the colon [2.22 (95% CI, 1.71-2.83) and 1.64 (95% CI, 1.09-2.39), respectively]. In patients with ulcerative colitis there was a significantly high risk of cancer of the rectum [1.84 (95% CI, 1.27-2.58)]. In patients with ulcerative colitis or Crohn's disease, who did not undergo partial or total colectomy for it, the rate ratios for colon cancer were, respectively, 5.52 (95% CI, 4.39-6.71) and 4.81 (95% CI, 3.52-6.47). In ulcerative colitis, there was an elevated risk of cancer of the rectum, liver and ovary. The rate ratio for lung cancer was low, but of borderline significance [0.72 (95% CI, 0.50-0.98)]. In Crohn's disease, the rate ratio was high for cancer of the cervix [2.63 (95% CI, 1.12-5.29)]. In patients with coeliac disease, the high-risk cancer was non-Hodgkin's lymphoma [rate ratio 3.28 (95% CI, 1.49-6.28)].

CONCLUSION

All three diseases carry an increased risk of cancer overall when the first year cases are included, though fairly modest in scale, and the increased risk seen in coeliac disease reduces when first year cases are excluded. Each has a distinctive pattern of individual high-risk cancers.

Monitoring singlet oxygen in situ with delayed chemiluminescence to deduce the effect of photodynamic therapy

Singlet oxygen ((1)O(2)) is an important factor mediating cell killing in photodynamic therapy (PDT). We previously reported that chemiluminescence (CL) can be used to detect (1)O(2) production in PDT and linked the signal to the PDT-induced cytotoxicity in vitro. We develop a new CL detection apparatus to achieve in vivo measurements. The system utilizes a time-delayed CL signal to overcome the interference from scattered excitation light, thus greatly improving the accuracy of the detection. The system is tested on healthy skin of BALB/ca mouse for its feasibility and reliability. The CL measurement is made during a synchronized gating period of the irradiation light. After each PDT treatment and in situ CL measurement, the skin response is scored over a period of 2 weeks. A remarkable relationship is observed between the score and the CL, regardless of the PDT treatment protocol. Although there are many issues yet to be addressed, our results clearly demonstrate the feasibility of CL measurement during PDT and its potential for in vivo PDT dosimetry. This requires further investigations.

Practical identifiability of photophysical parameters in photodynamic therapy

Photodynamic therapy (PDT) is an alternative treatment for cancer that involves the administration of a photosensitizing agent, which will be activated by light at a specific wavelength. In order to compare different photosensitisers for their cytotoxic activity, photophysical parameters provide good indicators. These parameters are generally estimated one by one from in vitro dedicated experiments, but they cannot always predict the in vivo cytotoxic action. So far, the estimation of photophysical parameters from in vivo data sets has never been regarded as a system identification problem. This paper deals with the practical identifiability of photophysical parameters. Practical identifiability deals with the uniqueness of the model parameters estimates, given the experimental data. The practical identifiability approach and its application to the photoreaction model of PDT are developed in this paper. It is shown that that the photophysical parameters involved in the kinetic model of photoreactions are identifiable in a practical framework with only one measurement - the intracellular photosensitizer concentration, and a wide square pulse as irradiation signal.

Photobleaching-based dosimetry predicts deposited dose in ALA-PpIX PDT of rodent esophagus

An improved method to estimate dose to esophageal tissue was investigated in the setting of photodynamic therapy with aminolevulinic acid-induced protoporphyrin IX (PpIX) treatment. A model of treatment-induced edema in the esophagus mucosa proved to be a well controlled and useful way to test the dosimetry model, and the light from the treatment laser together with the PpIX fluorescence intensity could be quantified reliably in real time. Dosimetry calculations based upon the detected fluorescence and bleaching kinetics were used to calculate the "effective" dose to the tissue, and a correlation was shown to exist between this metric and the edema induced in the esophagus. The difference between animals with no detectable treatment effect and those with significant edema was predictable based upon the dose calculation. The underlying assumption in the interpretation of the data is that rapid photobleaching of PpIX occurs when there is ample oxygen supply, and this bleaching is not present when oxygen is limited. This leads to the prediction that integration of the light and drug dose, in intervals where appreciable photobleaching occurs, should provide a prediction of the relative dose of singlet oxygen produced. This detection system and rodent model can be used for prospective dosimetry studies that focus on optimization of esophageal PDT.

Procedural Treatments for Acne Vulgaris

BACKGROUND

Simple procedural treatments such as comedone extraction and intralesional steroids have been utilized for many years as adjunctive therapy for acne. In the past 5 years, new technologies and procedures have become available that present new options for the treatment of acne.

OBJECTIVES

The objective was to review, summarize, and evaluate the key studies of procedural therapies for the treatment of acne as well as place them in perspective with current clinical practice.

METHODS

Studies selected for evaluation had at least 10 patients and clear statements of purpose, acne severity, patient selection, follow-up evaluations, previous and concurrent medications, treatment parameters, methods for evaluating results, and adverse effects. All studies were complete and published (in English) in peer-reviewed journals.

RESULTS AND CONCLUSIONS

Earlier procedural therapies were adjunctive to medical therapy, such as intralesional steroids, chemical peels, and microdermabrasion. Newer methods include radiofrequency, light or laser, and photodynamic therapy that represent treatment alternatives for systemic medications. Still early in their development, these new procedures provide an important, novel set of options for the treatment of acne. The most developed and studied therapies are blue or blue/red light combinations, 1,450-nm diode laser, and photodynamic therapy with 5-aminolevulinic acid or indocyanine green. Review of the literature of more up-to-date physical procedures provides a starting point for physicians seeking to treat their acne patients safely and effectively with these new methods.

Singlet oxygen luminescence dosimetry (SOLD) for photodynamic therapy: current status, challenges and future prospects

As photodynamic therapy (PDT) continues to develop and find new clinical indications, robust individualized dosimetry is warranted to achieve effective treatments. We posit that the most direct PDT dosimetry is achieved by monitoring singlet oxygen (1O2), the major cytotoxic species generated photochemically during PDT. Its detection and quantification during PDT have been long-term goals for PDT dosimetry and the development of techniques for this, based on detection of its near-infrared luminescence emission (1270 nm), is at a noteworthy stage of development. We begin by discussing the theory behind singlet-oxygen luminescence dosimetry (SOLD) and the seminal contributions that have brought SOLD to its current status. Subsequently, technology developments that could potentially improve SOLD are discussed, together with future areas of research, as well as the potential limitations of this method. We conclude by examining the major thrusts for future SOLD applications: as a tool for quantitative photobiological studies, a point of reference to evaluate other PDT dosimetry techniques, the optimal means to evaluate new photosensitizers and delivery methods and, potentially, a direct and robust clinical dosimetry system.

Protoporphyrin IX fluorescence photobleaching and the response of rat Barrett's esophagus following 5-aminolevulinic acid photodynamic therapy

Barrett's esophagus (BE) can experimentally be treated with 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT), in which ALA, the precursor of the endogenous photosensitizer protoporphyrin IX (PpIX) and subsequent irradiation with laser light are applied to destroy the (pre)malignant tissue. Accurate dosimetry is critical for successful ALA-PDT. Here, in vivo dosimetry and kinetics of PpIX fluorescence photobleaching were studied in a rat model of BE. The fluence and fluence rate were standardized in vivo and PpIX fluorescence was measured simultaneously at the esophageal wall during ALA-PDT and plotted against the delivered fluence rather than time. Rats with BE were administered 200 mg kg(-1) ALA (n = 17) or served as control (n = 4). Animals were irradiated with 633 nm laser light at a measured fluence rate of 75 mW cm(-2) and a fluence of 54 J cm(-2). Large differences were observed in the kinetics of PpIX fluorescence photobleaching in different animals. High PpIX fluorescence photobleaching rates corresponded with tissue ablation, whereas low rates corresponded with no damage to the epithelium. Attempts to influence tissue oxygenation by varying balloon pressure and ventilation were shown not to be directly responsible for the differences in effect. In conclusion, in vivo dosimetry is feasible in heterogeneous conditions such as BE, and PpIX fluorescence photobleaching is useful to predict the tissue response to ALA-PDT.

Cholecystectomy and endometrial cancer: a marker of long-term elevated estrogen exposure?

Excess hormones, both endogenous and exogenous, are implicated in the etiology of endometrial cancer. We considered whether having had gallstones or a cholecystectomy (surgery to remove the gallbladder), which are more common in women who are obese and who use exogenous hormones, might be a marker for high lifetime levels of estrogen. We conducted a population-based study of endometrial cancer cases and community controls in women aged 40-79 years. Participants completed an interviewer-administered questionnaire that elicited exposures prior to diagnosis or reference date, including history of gallstones and cholecystectomy, as well as reproductive history, lifetime body mass, smoking, postmenopausal hormone (PMH) use, and other risk factors. Compared to controls, cholecystectomy was associated with a 50% increased risk of developing endometrial cancer (odds ratio = 1.5 [1.1-2.0]). The relationship appeared to depend upon PMH user status; the association was observed only among never hormone users. Body mass index did not appear to modify this relationship. Having a diagnosis of gallstones was also associated with endometrial cancer, although to a lesser magnitude. Although other etiologic factors may play a role in the relation between cholecystectomy and endometrial cancer, the current analysis suggests that this association is attributable, at least in part, to the sharing of hormonal risk factors.

The use of photodynamic therapy for treatment of acne vulgaris

Current topical and most oral therapies for acne vulgaris have limited efficacy, especially in moderate to severe cases. Photodynamic therapy with 5-aminolevulinic acid and recently methyl aminolevulinate has been shown to be a safe and effective modality for the treatment of acne vulgaris. Consensus guidelines suggest that 30 to 60 minutes is sufficient 5-aminolevulinic acid contact time before photoactivation with blue light, red light, yellow light, broadband light, halogen, or pulsed dye laser devices. An average of three treatment can yield significant long-term improvement.

In vivo monitoring of singlet oxygen using delayed chemiluminescence during photodynamic therapy

It is known that singlet oxygen ((1)O(2)) is the main factor mediating cytotoxicity in photodynamic therapy (PDT). The effectiveness of a PDT treatment is directly linked to the (1)O(2) produced in the target. Although the luminescence from (1)O(2) is suggested as an indicator for evaluating photodynamic therapy, the inherent disadvantages limit its potential for in vivo applications. We have previously reported that chemiluminescence can be used to detect (1)O(2) production in PDT and have linked the signal to the cytotoxicity. We further our investigation for monitoring (1)O(2) production during PDT. The lifetime of 3,7-dihydro-6-{4-[2-(N(')-(5-fluoresceinyl)thioureido)ethoxy]phenyl}-2-methylimidazo {1,2-a} pyrazin-3-one-chemiluminescence (FCLA-CL) is evaluated, and the results show that it is much longer than that of direct luminescence of (1)O(2). A gated measurement algorithm is developed to fully utilize the longer lifetime for a clean measurement of the CL without the interference from the irradiation light. The results show that it is practically feasible to use the technique to monitor the (1)O(2). Compared to the direct (1)O(2) luminescence measurement, our new technique is sensitive and can be realized with a conventional optical detector with excellent signal-to-noise ratio. It thus provides a means for real-time in vivo monitoring of (1)O(2) production during PDT.

Incorporating Photodynamic Therapy into a Medical and Cosmetic Dermatology Practice

Effective in the treatment of a growing variety of skin conditions, photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) is rising rapidly in popularity among both practitioners and patients, despite the fact that many applications are not yet cleared by the Food and Drug Administration. Because of its versatility, safety, efficacy, cosmetic benefits, and potential financial advantages, ALA-PDT may soon be a mainstay in many clinical settings. This article provides an overview of this easy-to-use treatment modality and a guide to implementing ALA-PDT into practice, including pretreatment and post-treatment protocols and guidelines for managing side effects.

Monitoring of Singlet Oxygen Is Useful for Predicting the Photodynamic Effects in the Treatment for Experimental Glioma

PURPOSE

Singlet oxygen ((1)O(2)) generated in photodynamic therapy (PDT) plays a very important role in killing tumor cells. Using a new near-IR photomultiplier tube system, we monitored the real-time production of (1)O(2) during PDT and thus investigated the relationship between the (1)O(2) production and photodynamic effects.

EXPERIMENTAL DESIGN

We did PDT in 9L gliosarcoma cells in vitro and in an experimental tumor model in vivo using 5-aminolevulinic acid and nanosecond-pulsed dye laser. During this time, we monitored (1)O(2) using this system. Moreover, based on the (1)O(2) monitoring, we set the different conditions of laser exposure and investigated whether they could affect the tumor cell death.

RESULTS

We could observe the temporal changes of (1)O(2) production during PDT in detail. At a low fluence rate the (1)O(2) signal gradually decreased with a low peak, whereas at a high fluence rate it decreased immediately with a high peak. Consequently, the cumulative (1)O(2) at a low fluence rate was higher, which thus induced a strong photodynamic effect. The proportion of apoptosis to necrosis might therefore be dependent on the peak and duration of the (1)O(2) signal. A low fluence rate tended to induce apoptotic change, whereas a high fluence rate tended to induce necrotic change.

CONCLUSIONS

The results of this study suggested that the monitoring of (1)O(2) enables us to predict the photodynamic effect, allowing us to select the optimal laser conditions for each patient.

Feasibility of using fluoresceinyl Cypridina luciferin analog in a novel chemiluminescence method for real-time photodynamic therapy dosimetry

Singlet oxygen ((1)O(2)) is the most important cytotoxic agent in photodynamic therapy (PDT). The feasibility of using a chemiluminescence (CL) probe, 3,7-dihydro-6-[4-(2-(N'-(5-fluoresceinyl)thioureido)ethoxy)phenyl]-2-methylimidazo{1,2-a}pyrazin-3-one sodium salt (fluoresceinyl Cypridina luciferin analog, FCLA), to monitor (1)O(2) production during PDT is evaluated in vitro. Lymphoma cells were treated with various protocols of PDT. The results show that the FCLA-CL production during PDT is linearly related to the corresponding cytotoxicity, regardless of the treatment protocol. With minimum cytotoxicity and interference to the PDT treatment outcome, the FCLA-CL system is an effective means to quantify PDT (1)O(2) production and may provide an alternative real-time dosimeter.

Pretreatment photosensitizer dosimetry reduces variation in tumor response

PURPOSE

To compensate for photosensitizer uptake variation in photodynamic therapy (PDT), via control of delivered light dose through photodynamic dose calculation based on online dosimetry of photosensitizer in tissue before treatment.

METHODS AND MATERIALS

Photosensitizer verteporfin was quantified via multiple fluorescence microprobe measurements immediately before treatment. To compensate individual PDT treatments, photodynamic doses were calculated on an individual animal basis, by matching the light delivered to provide an equal photosensitizer dose multiplied by light dose. This was completed for the lower quartile, median, and upper quartile of the photosensitizer distribution. PDT-induced tumor responses were evaluated by the tumor regrowth assay.

RESULTS

Verteporfin uptake varied considerably among tumors and within a tumor. The coefficient of variation in the surviving fraction was found significantly decreased in groups compensated to the lower quartile (CL-PDT), the median (CM-PDT), and the upper quartile (CU-PDT) of photosensitizer distribution. The CL-PDT group was significantly less effective compared with NC-PDT (Noncompensated PDT), CM-PDT, and CU-PDT treatments. No significant difference in effectiveness was observed between NC-PDT, CM-PDT, and CU-PDT treatment groups.

CONCLUSIONS

This research suggests that accurate quantification of tissue photosensitizer levels and subsequent adjustment of light dose will allow for reduced subject variation and improved treatment consistency.

Light dosimetry measurements during ALA-PDT of Barrett's oesophagus

A fibre optic probe and compact light detection system has been used to monitor the fluence-rate at the tissue surface during 5-aminolaevulinic acid based photodynamic therapy (PDT) of Barrett's oesophagous. The contributions from three specific wavelengths were recorded, corresponding to the combination of therapeutic laser light and fluorescence emission from protoporphyrin IX (635nm), the fluorescence from an oxidation product of the photosensitiser (670nm), and the protoporphyrin IX fluorescence alone (705nm). We have found that light scattering results in an enhancement of the therapeutic fluence-rate, and hence light dose, by approximately 70%. At the onset of therapy the fluorescence provides a 10% contribution to the overall fluence-rate at 635nm. The dynamics of photosensitiser bleaching could be extracted from the depletion in light signals. By defining a bleaching dose as the 635nm light fluence delivered over the period during which the photosensitiser fluorescence decays to 1/e(3) of its initial value, we find that the average ratio of bleaching to total dose is 33%. Further, the fluorescence contributes approximately 5% of the bleaching light dose. These results suggest that the prescribed period of therapeutic light exposure may be reduced with no loss in clinical efficacy, but with a consequent improvement in patient tolerance to this therapy.

Local physiological changes during photodynamic therapy

BACKGROUND AND OBJECTIVE

Herein an overview is provided of the causes, consequences, and significance of photodynamic therapy (PDT)-mediated effects on tumor oxygenation and blood flow during illumination.

STUDY DESIGN/MATERIALS AND METHODS

Techniques particularly valuable to this research have included tissue oxygen tension measurement by the Eppendorf pO2 Histograph; spatial quantification of hypoxia by EF3 and EF5; and tissue oxygenation/blood flow monitoring by diffuse reflectance/correlation spectroscopy.

RESULTS

Severe hypoxia was measured in vivo during PDT and is shown to be a consequence of photochemical oxygen consumption and/or compromised vascular perfusion. Oxygen depletion can be controlled by treatment regimen, occurs in a spatially-definable pattern, and is therapy-limiting. PDT-induced changes in tumor oxygenation during illumination are correlated with outcome. In PDT-treated tissues, blood flow also is determined by treatment regimen and correlates with treatment response.

CONCLUSIONS

Photodynamic therapy creates distinct, measurable changes in tumor oxygen and blood flow during illumination. These physiological changes may ultimately affect treatment efficacy.

Enhancement of Fluoresceinyl Cypridina Luciferin Analog Chemiluminescence by Human Serum Albumin for Singlet Oxygen Detection

Fluoresceinyl cypridina luciferin analog (FCLA) is a chemiluminescence (CL) probe for detecting reactive oxygen species (ROS). Its efficiency for detecting singlet oxygen (1O2) can be significantly enhanced in the presence of human serum albumin (HSA). This phenomenon may apply to important applications for both research and clinical testing, because of the broad presence of HSA in the human system. In the current study the mechanism of the FCLA-HSA CL system is studied by means of direct CL measurement and spectroscopy techniques. Our results show that FCLA can combine with HSA via a single binding site to form a complex. The CL efficiency of the system is largely governed by an intersystem energy transfer between the two components upon interaction with 1O2. The CL production reaches maximum in a synergetic manner when equal amounts of FCLA and HSA are present simultaneously, but production is less at other ratios. The results also show that the combination of FCLA with HSA does not significantly alter the ROS selectivity of FCLA. In conclusion, our study shows that FCLA and HSA can combine and form a complex with higher CL efficiency. This provides us a new approach in designing CL techniques for studying ROS.