Patent Application: US-64124000-A

Abstract:
bacterial spores can be rapidly and sensitively detected and quantified based upon molecular recognition of unique chemicals in the spore coat . spores can be detected and assayed based upon the calcium concentration in bacterial spore coats using the calcium which is unique to the bacterial spores . since spores contain a high concentration of calcium relative to other biological materials , fluorescent calcium - sensitive indicators are used to detect ca + 2 displaced from the spore case or free in solution or from the aerosol phase . visibly excitable fluorescent dyes provide a sensitive and selective means to monitor changes in spore concentration and avoid difficulties associated with laser or uv - excitation .

Description:
the spore detection scheme of the present invention uses a sensor created by combining a fluorescent calcium - sensitive indicator , such as calcein in a viscous membrane on planar coupons . the coupons are preferably made of silica glass . the sensor coupon is affixed to the distal end of an optical fiber , which provides excitation light and collects the fluorescence emission . aqueous micro - droplets of bacterial spores are added to the sensor , and the resulting increase in fluorescence intensity is monitored this assay is based on the high concentration of calcium dipicolinic acid complex unique to bacterial spores , and the use of fluorescence spectroscopy to detect and quantify spore concentration . this sensor technology is applicable to near real - time detection of bacterial spores without interference from light scattering or other ambient biological materials such as bacteria , pollen , viruses , and fungal spores . while micro droplets are not essential , a totally dry environment will not support the reaction . aerosolized spores that deposit onto a film , e . g ., glycerol / calcein , can be detected by this method . a number of different molecular probes can be used to detect the calcium in bacterial spores according to the present invention , including fluorescent calcium indicators excited with ultraviolet light , fluorescent calcium indicators excited with visible light , and fluorescent calcium indicator conjugates . nonlimiting examples of some of these indicators are shown below : as shown in fig5 light scattering off the dense spore coat is characterized by comparing the signal from 0 . 75 mm - diameter polystyrene beads [ a mimic of the spore shape and size ( 1 - 2 mm in diameter )] and spore suspensions . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . if light scattering off the spore coat is a factor , then the signal should be detectable with the addition of polystyrene beads . in this case , when compared to the fluorescence intensity of spore concentration , the fluorescence signal intensity of the beads was virtually negligible . these results indicate that light scattering off the spore coat is not a factor in this assay . the reactivity of the spores was characterized by exposing the spores to chemistries containing calcium indicators or dna probes . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . the fluorescence intensity resulting from the chemistry containing the dna probe was virtually zero compared to the chemistry containing a calcium - sensitive indicator . the data , shown in fig6 demonstrate the inability to stain spores using dna probes . the reactivity of the bacteria was characterized by exposing the bacteria to chemistries containing calcium indicators or dna probes . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . the fluorescence intensity resulting from the chemistry containing the calcium - sensitive indicator was negligible compared to the chemistry containing a dna probe . the data , shown in fig7 demonstrate the specificity of the calcium indicators for spores . the sensor configuration is shown in fig1 a and 1b , using an acton research corporation spectrapro ( r ) double monochromator 100 . light from a xenon lamp 101 is collimated , passed through an excitation filter 103 and beamsplitter 105 , and focused with a 16 × microscope objective 106 on the proximate end of an 800 micron diameter optical fiber 107 . the incident excitation light is propagated through the fiber to the fluorescent probe and collected back through the fiber , reflected off the beam splitter , focused by a lens 104 , passed through an emission filter and detected by a photomultiplier tube 102 . as shown in fig1 b , the sample 110 is pipetted onto a planar glass coupon 109 and positioned on the platform 108 so that the micro - droplet of sample completely covers the distal end of the optical fiber . the initial step in developing an assay for spore detection was to determine the sensitivity , or limit of detection , of the sensing chemistry toward ca 2 + ions . a calibration curve of cacl 2 concentration with the least squares fit is shown in fig2 . the correlation coefficient , r 2 , is 0 . 9937 . the limit of detection was calculated by dividing three times the standard deviation of the control ( no cacl 2 ) by the slope of the curve , yielding a value of 35 nm ca 2 + . since the calculated concentration of ca 2 + in a suspension of 1 . 8 e7 spores per ml is approximately 45 nm , the sensing chemistry has sufficient sensitivity to detect bacterial spores . the second step in developing the assay was to define the spectral response curves resulting from spore / dye interactions . the spectral changes with varying spore concentration are shown in fig3 showing that the peak fluorescence emission at 515 nm decreases with decreasing spore concentration . once the spectral characteristics of the assay were determined , further data were taken with a time - based acquisition by setting the excitation and emission wavelengths at their maxima ( 485 nm and 515 nm , respectively ) and integrating over time . collecting the raw signal data via time - based acquisition rather than collecting the entire spectrum greatly reduces the measurement time and improves the reproducibility of the measurement ( i . e ., less photo bleaching of the indicator dye ). fig3 shows a calibration curve with the least squares fit of spore concentration that determines the sensitivity or limit of detection ( lod ) of the sensing chemistry toward spores . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement ( no spores ) was subtracted from all data points to eliminate background fluorescence . the correlation coefficient , r 2 , is 0 . 9928 . the lod was calculated by dividing 3 times the standard deviation of the control ( no spores ) by the slope of the curve . the calculated lod of this assay is 1763 spores . the spectral response curves resulting from spore / dye interaction are shown in fig4 . the data were collected using a 495lp emission filter , setting the excitation wavelength at 485 nm , and measuring the resulting fluorescence for 300 ms over a wavelength range of 500 - 600 nm . the peak fluorescence emission intensity occurs at 515 nm . spectral data were analyzed by averaging the spectra of three replicates . a control measurement , no spores , was subtracted from all data points to eliminate background fluorescence . although there is an immediate increase in fluorescence intensity when the spores are added to the sensing chemistry , the spores were allowed to incubate for 20 minutes . by incubating the spores for 20 minutes , the maximum fluorescence intensity increase is monitored without effects from evaporation of the micro droplet . the immediate change in fluorescence signal can be used as the basis for a real - time warning device . the sensors of the present invention are intended for use in the field , and therefore the sensor response to potential interferents was characterized to avoid false positive or ambiguous results . one effect that may interfere with the sensor signal is light scattering off the dense spore coat . this effect was measured in two ways . first , the spore suspensions were replaced with 0 . 75 micron diameter polystyrene beads . the beads served as a mimic of the spore shape and size , i . e ., ˜ 1 micron in diameter . the resulting fluorescence intensity signal from the bead suspensions was negligible . second , spore suspensions were introduced to the sensor without the indicator dye present . if light scattering by the spores were a factor , then the signal should be detectable even without the indicator dye present . in this case , the fluorescence signal intensity was virtually zero . these results indicated that light scattering by the spores is not a factor in this assay , as shown in fig5 . fig6 shows the reactivity of spores to calcium indicators versus dna probes . the reactivity of the spores was characterized by exposing the spores to chemistries containing calcium indicators or dna probes . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . the fluorescence intensity resulting from the chemistry containing the dna probe was virtually zero compared to the chemistry containing a calcium sensitive indicator . the data demonstrate the inability to stain spores using dna probes . fig7 illustrates the reactivity of bacteria to calcium indicators versus dna probes . the reactivity of the bacteria was characterized by exposing the bacteria to chemistries containing calcium indicators or dna probes . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . the fluorescence intensity resulting from the chemistry containing the calcium - sensitive indicator was negligible compared to the chemistry containing a dna probe . the data demonstrate the specificity of the calcium indicators for spores . the fluorescence of free tb 3 + and ca 2 + were compared to the intensity from spore suspensions in bulk solution , as shown in fig8 . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement was subtracted from all data points to eliminate background fluorescence . the fluorescence increase from the free ions of tb 3 + and ca 2 + to spore suspensions is 510 % and 1095 %, respectively , as shown in fig8 . the effect of buffer on the sensing chemistry was characterized by preparing a calibration curve of ca 2 + in water versus ca 2 + in tris buffer . the data were analyzed by averaging the integrated signal from three replicates and calculating the standard deviation . a control measurement ( no ca 2 + ) was subtracted from all data points to eliminate background fluorescence . the fluorescence intensity response of ca 2 + buffer to calcein dye fell below the background measurement , as shown in fig9 indicating that there is a significant buffer effect when compared to data taken in a water environment . the fluorescence signal from calcein in the presence of metal ions is ph dependant at very basic ph . therefore , the effect of ph on the sensing chemistry was also tested . to test the ph effect , sensors were prepared by substituting trizma ( r ) buffer at ph 6 . 5 , 7 . 4 , or 9 . 0 for the water . calibration curves of ca 2 + ion concentration at each ph were developed . the linearity of the curve was unaffected by the preparations at neutral and acidic ph . as shown in fig1 , elevated ph greatly altered the linearity of the curve . this correlates to previously published data detailing the ph dependence of calcein dye at basic phs ( wallach ). since the likelihood that spores will be present in a highly basic solution is low , the ph dependence at basic phs should not be a factor in the practical implementation of sensing spores . table 2 shows the effects of potential interberents on the sensor . the data were compiled by averaging the background subtracted integrated intensity data from a minimum of three separate experiments ( different chemistry preparations ) to generate a representative fluorescence intensity value for pseudomonas aeruginosa bacteria , ms 2 bacteriophage ( a viral bw simulant ), ragweed pollen , and penicillium roquefortil mold spores . the normalized average integrated intensity of each material is relative to the spore values ( 100 %). all of the biological interferents yield a normalized fluorescence intensity of 20 % or less indicating that there is minimal interference in the sensor from other biological materials . the sensor of the present invention combines a visibly excitable , fluorescent , calcium - sensitive indicator with optical fibers and disposable planar glass coupons to create a rapid , cost - effective and simple sensor . the advantages of the sensor of the present invention are threefold : 1 . the ability to incorporate multiple sensors per coupon and directly measure the sample fluorescence without further washing or filtering steps dramatically decreases analysis time and reduces possible sources of error compared to conventional microbiological methods . 2 . using visibly excitable indicators effectively overcomes limitations introduced by laser and uv excitation sources required by other detection methods . 3 . cross - reactivity with other biological materials such as bacteria , pollen , viruses , and mold as well as interference from light scattering and ph , are negligible . many conventional detection technologies are hindered by time - consuming measurements , bulky equipment that is both costly and power consumptive , an d / or cross - reactivity with other biological materials . the speed , simplicity , and selectivity of the assay of the present invention , however , are advantageous for developing a hand - held or field portable bacterial spore detection and warning device . depending upon the user &# 39 ; s particular requirements , any type of warning indicator can be used with sensors according to the present invention . nonlimiting examples of such warning devices include audible and visible warning devices , such as bells , sirens , lights , and the like . the foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can , by applying current knowledge , readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept , and , therefore , such adaptions and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments . it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation . 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