in the following description , reference is made to the accompanying drawings , which form a part hereof , and which show , by way of illustration , specific embodiments or processes in which the teachings of the present disclosure may be practiced . where possible , the same reference numbers are used throughout the drawings to refer to the same or like components . in some instances , numerous specific details are set forth in order to provide a thorough understanding of the present disclosure . the teachings of the present disclosure , however , may be practiced without the specific details or with certain alternative equivalent devices and methods to those described herein . in other instances , well - known methods and devices have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure . fig1 illustrates the system overview and components of an embodiment of the transmission fluorometry system 100 of the present disclosure . in the embodiment shown in fig1 , the system 100 comprises a power supply 110 coupled to a light source driver control 120 . the light source driver control 120 is coupled via any suitable electrical connection 190 to a source - receiver assembly 130 , which comprises a light source 140 and receiving optics 160 . a spectrometric assembly 170 can be coupled to the receiving optics 160 via any suitable optical link 195 for providing a spectral data output of the light transmitted through and / or emitted from the sample 150 . the spectral data 170 can be fed into a computer 180 for analysis . in operation , the power supply 110 powers light source driver control 120 . any suitable power supply can be employed . examples of suitable power supplies that can be employed include battery power , usb cable , and / or electrical outlet power . the type of power supply 110 may depend on the intended use of the system 100 and can potentially enhance the convenience of employing the system 100 , for example , if the system 100 is used only to take absorption measurements versus fluorescent measurements , it can run on battery power for relatively long periods of time ( e . g . several days of continuous operation , depending on the battery technology employed ). the system 100 can also be powered from the usb port of a personal computer 180 . this is a convenient arrangement when the goal is , for example , to continuously upload readings from the spectrometric assembly 170 over the same usb cable , because it means that the system 100 does not require any extra external power connection . it is also convenient when the system 100 needs to be taken out in the field , because the user can then view the system 100 as a peripheral ( much the same way as a usb memory stick is viewed as a peripheral ) that simply attaches to the computer 180 . the power supply 110 can run off of wall current if , for example , the goal is to provide continuous monitoring over a long period of time . the light source driver control 120 drives one or more excitation light sources 140 , mounted on the source - receiver assembly 130 . any suitable light source driver can be employed . for example , the light source driver control 120 can be a manual system of switches and potentiometers or an automatic electronic system controlled from the computer 180 in a closed loop configuration . in an embodiment , the computer 180 provides continuous monitoring of the sample 150 and adjusts the light source 140 brightness via the automatic electronic system based on how much light is being transmitted through the sample 150 , as well as how much fluorescence is being detected by the receiving optics 160 . in this case , a control loop 185 for controlling the light source can be driven automatically without any manual intervention whatsoever . the source - receiver assembly 130 contains a light source 140 that irradiates the sample 150 , which in turn transmits both light from the light source 140 and fluoresced light from analytes in the sample 150 . this light is detected by the receiving optics 160 which provides input to a spectrometric assembly 170 . in an embodiment , the source - receiver assembly can contain one or more led light sources 140 . light from the light source 140 can excite several analytes in the sample 150 and passes a single spectrum via the receiving optics 160 to the spectrometric assembly 170 . the receiving optics 160 may comprise , for example , a collimating lens that connects to the spectrometric assembly 170 via a fiber optic cable 195 . in an embodiment , light source 140 can be configured as a set of leds clustered together on a single clip arm or a single chip substrate . the leds can be turned on and off in sequence , exciting a series of spectrums in the sample 150 that pass through the receiving optics 160 and are transmitted to the spectrometric assembly 170 . in this manner , it is possible to detect multiple components using multiple excitation wavelengths . for example , a sensor head containing both a 425 nm led and a 346 nm led can be used to non - invasively detect zinc protoporphyrin and retinol ( vitamin a ) simultaneously . in one embodiment , the source - receiver assembly 130 can be configured as a sample holding device , illustrated in fig4 , that pinches the sample between the light source 140 and the receiving optics 160 . the decoding and analysis of the set of spectrums can then be done by the computer 180 . the source - receiver assembly can include , for example , a sample holding device 400 having an upper arm 430 and a lower arm 440 . fig4 illustrates a sample holding device 400 in an open position 410 and a closed position 420 . the source - receiver assembly 130 may include a set of sample holding devices 400 , as shown in fig5 , each with a single or multiple led light source 140 , as described previously . this configuration can be used if , for example , the tester wants to take simultaneous measurements of different parts of the subject 150 at the same time . if the tester wants a narrowed spectrum light , the source - receiver assembly 130 can employ laser diodes as light sources 140 in place of the leds . if the tester wants more exact wavelength control , the source - receiver assembly 130 can employ a traditional monochromator as a light source 140 . the spectrometric assembly 170 can be a single spectrometer , such as an oceanoptics usb2000 , which connects to the computer 180 via , for example , a usb port . an alternate embodiment is a spectrometric assembly 170 with a set of photodiode / filter pairs where each pair is tuned to either the excitation wavelength or fluorescent emission peaks of analytes of interest . for high resolution applications , a high sensitivity version of the spectrometric assembly 170 can employ a single photomultiplier tube or charge coupled device ( ccd ) array , and the filters can be successively passed over the active area of the receiving optics in order make the device sensitive to the wavelengths of interest . in light of the disclosure herein , providing any of the above mentioned spectrometric assemblies is well within the ordinary skill of the art . the spectrometric assembly 170 is linked to a computer 180 . the computer 180 can be a “ personal computer ” running spectrographic analysis algorithms . however , in the event the tester wants to provide continuous monitoring in a small form factor , the computer 180 can be a micro - controller , such as , for example , a member of the texas instruments msp430fg43x : mixed signal microcontroller family . in this case , the computer 180 can , for example , monitor the input spectrum from the spectrometric assembly 170 , control the light source 140 through the light source driver control 120 via the control loop 185 , analyze the spectrum and convert the results to human readable form . fig2 illustrates a signal processing functional diagram 200 , according to an embodiment of the present disclosure . a closed - loop control function 210 passes an electric - digital control representation 213 to an electric - digital to electric - analog conversion function 220 . the electric - digital to electric - analog conversion function 220 passes an electric - analog representation 223 to an electric - analog to optical conversion function 230 . the electric - analog to optical conversion function 230 generates an incident optical signal 233 which is directed to a first surface of the sample 150 . an optical signal 238 emerging from a second surface of the sample 150 is received by an optical to electric - analog conversion function 240 . the optical to electric - analog conversion function 240 passes an electric - analog representation 243 to an electric - analog to electric - digital conversion function 250 . the electric - analog to electric - digital conversion function 250 passes an electric - digital representation 253 back to the closed - loop control function 210 . a high level data collection and computing function 260 communicates with the closed - loop control function 210 through an interface function 263 . in operation , an embodiment of the dosed loop control function 210 can be configured to provide control instructions for the electric - digital to electric - analog conversion function 220 , the electric - analog to optical conversion function 230 , data gathering for the optical to electric - analog conversion function 240 and the electric - analog to electric - digital conversion function 250 . the closed loop control functions can be either manual or automatic . any suitable closed - loop control function can be employed . a manual control function uses an operator to read feedback parameters such as noise and received light intensity at particular wavelengths and computed functions thereof ( e . g . spo 2 level ) and to manually adjust the incident light intensity , duration and physical and temporal point of measurement in order to get a strong signal that does not swamp the receiving optics . an automatic control function is performed automatically in real - time and can be implemented using micro controllers such as , for example , atmel &# 39 ; s avr or texas instrument &# 39 ; s msp430 . in one embodiment , the closed loop control function 210 can be a pulse oximeter , which can take , for example , red and infrared light absorption readings every 1 ms using a standard pulse oximetry probe . these readings can be smoothed by the closed loop control function 210 and transmitted to the high level data collection and computing function 260 in order for the system to monitor and record sample data . the closed loop control function 210 may also receive commands from the high level data collection and computing function 260 , allowing it , for example , to take additional readings with other wavelengths , at desired points in time and for desired durations . in an embodiment , the electric - digital to electric - analog conversion functions 220 can be used to convert a digital control representation 213 to an analog representation 223 . in one embodiment , the digital control representation 213 may be used to select a desired light source and an associated intensity with which to illuminate the sample . in this case , the electric - digital to electric - analog conversion function 220 may convert the digital control representation 213 to a set of analog signals at various voltage or current levels ( including zero ) to drive the electric - analog to optical conversion function 230 . the electric - digital to electric - analog conversion function 220 can be performed with a digital to analog converter ( dac ). the dac may be a standalone unit , or integrated with the closed loop control function 210 as in the case of , for example , the msp430 . in an embodiment , the electric - analog to optical conversion function 230 can be used to convert the analog electrical representation 223 to the light signal that illuminates the sample . this function can be implemented for example as one or more leds or laser diodes mounted on a semiconductor chip , as a bundle of fibers connecting to an array of leds or laser diodes mounted on a board , or as a single light source with a switchable set of filters . the electric - analog to optical conversion function 230 may be for example a standalone unit , or integrated with the optical to electric - analog conversion function 240 as in the case of , for example , a nellcor pulse oximeter probe . in an embodiment , the optical to electric - analog conversion function 240 is used to convert the light signal that is received from the sample 150 to an electric - analog representation 243 . the optical to electric - analog conversion function 240 can be , for example , a photodiode as used in a pulse oximeter ; a diffraction grating and ccd array as used in a spectrometer , such as the oceanoptics usb 2000 ; or a photomultiplier tube , such as used in a fluorimeter . the optical to electric - analog conversion function 240 may be a standalone unit , or integrated with the electric - analog to electric - digital conversion function 250 , as used , for example , in an oceanoptics spectrometer . in an embodiment , the electric - analog to electric - digital conversion function 250 can be used to convert an analog representation 243 to a digital control representation 253 . in an embodiment , this conversion can be an analog to digital converter ( adc ). the electric - analog to electric - digital conversion function 250 may be , for example , a standalone unit , or integrated with the closed loop control function 210 as in , for example , the texas instrument &# 39 ; s msp430 . in an embodiment , the high level data collection and computing function 260 can communicate with the closed - loop control function 210 to transmit instructions and receive and store data . the high level data collection and computing function 260 can be any suitable computing device such as , for example , a personal computer , a handheld computer or a laptop computer . the functions closed - loop control 210 , electric - digital to electric - analog conversion 220 , electric - analog to electric - digital conversion 250 , and high level data collection and computing 260 , could potentially be performed manually by an operator , but any such embodiments would be of little value compared to automated functions offered by modern technology . fig3 illustrates an embodiment of the light source driver control 120 . current from the power supply 110 flows through power switch 310 , which controls when power is applied to the source - receiver assembly 130 to excite the sample and generate a fluorescent output characteristic of the analytes to be measured . the light source selector switch 320 provides flexibility to select any configuration of light sources 140 that may be appropriate to optimize a particular application . the intensity of each light source 140 can be independently controlled by a light source intensity controller 330 , either manually or automatically . in one embodiment , the light source intensity can be automatically set by a control algorithm running on the computer 180 to a desirable level that optimizes the dynamic range and signal to noise ratios of the detected excitation and / or the analyte spectral signals . in an embodiment , the intensity controllers 330 can be connected to light source connectors 340 , which can provide for a desired connectability to the light source 140 ( e . g ., leds ). fig4 illustrates an embodiment of the source - receiver assembly 130 in the form of a sample holding device 400 . the sample holding device 400 is illustrated in both an open position 410 and a closed position 420 . the sample 150 to be measured can be held between one or more light sources 140 mounted on the upper arm 430 of the sample holding device 400 and the receiving optics 160 mounted on the lower arm 440 of the sample holding device 400 . employing appropriate sample thicknesses can allow for the desired transmission of light ( e . g ., light from the light source 140 and / or fluoresced light ) through the sample . for example , sample thicknesses can be consistent with a desired resolution of quantitative measurements of intensity of both excitation light transmitted through the sample and the fluoresced light emitted by blood analytes upon excitation by the light source . examples of samples for which the clip mechanism is desirable include : a thin film , the webbing between a subject &# 39 ; s index finger and thumb , the subjects ear , the subject &# 39 ; s nose , the subject &# 39 ; s cheek , a section of loose skin on a subject &# 39 ; s wrist or elbow joint or any other part of the subjects body where a desired sample thickness can be identified . when applying the sample holding device 400 to a subject for blood testing , the pressure blanches the skin , resulting in a dilution effect of the blood in the sample , which minimizes inner filtering . a light source connection device 450 can provide a connection to light source driver control 120 . a receiving optics connection device 460 can provide a connection to the spectrometric assembly 170 . fig4 also shows a “ c ” clamp 470 to illustrate a mechanism to control the sample thickness by compressing the gap between the upper and lower arm of the sample holding device 400 . also shown are an adjustment knob 475 and a side view of the “ c ” clamp 480 . in other embodiments , the mechanism to control the sample thickness can use a variety of modern technologies . examples of such technologies include : a piezoelectric crystal based system attached to the arm , a hydraulic based system consisting of a pressurized liquid filled cylinder and a pneumatic based system with a pressurized air filled bag . an additional advantage of these modern technologies is the capability to provide a way to control sample thickness without completely blanching the tissue . the mechanism to control the sample thickness may improve the results obtained using the system of the present application for cases where the wavelengths of interest are heavily attenuated by the sample . for example , measurements of zinc protoporphyrin ( zpp ) at wavelengths in the ranges of 346 to 370 nm , 390 to 400 nm and 420 to 430 nm in a sample of in vivo skin , can be more reliably obtained where the skin can be pinched to a suitable thickness . in accordance with the beer - lambert law , the attenuation of light within the sample increases exponentially with the sample thickness and analyte concentration . the use of a sample holding device configured to provide controlled reductions of the sample thickness can have two beneficial effects . it can cause a reduction of the sample thickness while at the same time it may also reduce the concentration of analytes by a blanching process . while not intending to be limited by theory , it is believed that a significant increase in detected intensity can be achieved due to one or more of these benefits . for example , a ½ ″ thick sample of hemoglobin irradiated with 10 lumens of light at 940 nm will produce an output intensity of approximately 0 . 00263 lumens . for comparison , a comparable output intensity can be obtained with a 1 / 16 ″ inch thick sample of hemoglobin that has been diluted by a factor of 32 by blanching and is irradiated with the same 10 lumens of light at 426 nm . these considerations illustrate a potential advantage of the aforementioned sample holding device , which is that it can allow transmission fluorimetry to determine analyte concentration ratios via light absorption and fluorescence at wavelengths outside of the “ medical spectral window ” of 600 - 1100 nm . thus , the systems of the present application can employ wavelengths of less than 600 nm , such as for example , wavelengths in the ranges of 346 to 370 nm , 390 to 400 nm and 420 to 430 nm . wavelengths outside of these example ranges can also be employed , including wavelengths within the medical spectral window . although fig4 shows a very simple mechanism to control the sample thickness , other implementations can use more desirable systems to achieve the objectives outlined herein , such as reducing sample thickness and / or blanching the sample . in light of the disclosure herein , providing any of the above mentioned thickness control systems is well within the ordinary skill of the art . fig6 is a flowchart illustrating a preferred method 600 by which the transmission fluorometry system 100 can collect normalized fluorometry data from a sample . at 601 , the source - receiver assembly 130 is applied to the sample 150 . at 602 , power is applied to the light source 140 . at 603 , the output from the spectrometric assembly 170 is transmitted to the computer 180 . at 604 , a computer program is run . the computer program can compute , for example , the relative concentrations of two or more analytes present in the sample 150 based upon spectral outputs collected by the spectrometric assembly 170 . in an embodiment , analyte ratios can be computed by using “ absorption only ” techniques such as those used by pulse oximeters . for example pulse oximeters compute heart rate and blood o 2 concentration using measurements of the relative absorption of blood and surrounding tissue at two different wavelengths over time . in another embodiment , these analytes may be computed by using “ fluorescence only ” techniques , such as algorithms that look at the ratios of emission heights from the same excitation wavelength . the ratios of the heights of multiple emission peaks can be calculated . exemplary ratios include the ratio of primary to secondary emission peaks of the analyte zinc protoporphyrin when excited at 425 nm or the ratio of the primary emission peak of zinc protoporphyrin to protoporphyrin ix when both are excited at 365 nm . in yet another embodiment , a technique employing a ratio of ratios can used , which compares the ratio of one set of excitation and emission peaks to the ratio of another set of excitation and emission peaks . calculating a ratio of ratios is generally well known in the art . in yet another embodiment , analytes may be computed by using “ mixed absorption and fluorescence ” techniques , such as one that would look at the ratios of emission heights to absorption ratios which occur when the same tissue is irradiated by two or more light sources that are placed very near each other . an example is the ratio of hemoglobin absorption to zpp fluorescence relative to the ratio of their respective irradiation light intensities . these analytes may also be computed by using “ time resolved methods ” or “ frequency resolved methods ”. for example , one such method distinguishes between two analytes with similar spectral signatures by measuring their fluorescent lifetimes . given the present disclosure , one of ordinary skill in the art would be able to employ the systems disclosed herein to detect analytes using absorption only , fluorescence only and mixed absorption and fluorescence techniques . fluorometry data taken from the sample can be normalized to allow different readings taken independently to be compared . any suitable method of normalizing the data can be employed . fig7 illustrates an embodiment of a sample normalization algorithm 600 . a spectrometric assembly 170 organizes data in terms of a graph of relative intensity 710 versus wavelength 720 . for illustrative purposes , relative intensity 710 can be an integer that ranges from 0 to a maximum relative intensity 760 of 4095 , as depicted in fig7 . to allow intensity data from different light sources 140 examining the same subject at the same time to be compared to each other , the intensity can be normalized . this is done by first determining the “ minimum relative intensity ” 730 , which is the smallest intensity recorded by the spectrometric assembly 170 for the sample 150 . next , the “ excitation relative intensity ” 740 is determined by looking up the intensity at the excitation wavelength 770 . finally , a normalized intensity value is calculated at each wavelength by taking the relative intensity reading at that wavelength , subtracting the minimum relative intensity 730 , and dividing this difference by the difference between the excitation relative intensity 740 and the minimum relative intensity 730 . if done for each wavelength , this algorithm will produce a graph of normalized intensities 750 where the intensity at the excitation wavelength 770 will have a value of “ 1 . 00 ” with all other intensities scaled relative to it . although this invention has been described in terms of certain preferred embodiments , other embodiments that are apparent to those of ordinary skill in the art , including embodiments that do not provide all of the features and advantages set forth herein , are also within the scope of this invention . therefore , the scope of the present invention is defined only by reference to the appended claims and equivalents thereof .
this disclosure relates generally to a system and method for noninvasive , non - destructive fluorescent measurement . more specifically , the disclosure provides a non - invasive metrology system and method to monitor levels of fluorescent chemicals in the blood . a major application for the invention is field - based non - invasive blood testing for micro - nutrient deficiency and diseases resulting from it , such as iron deficient anemia . the invention may help reduce or eliminate the need for blood drawing , sending the sample to a blood lab and having to wait for a result .