1. School of Chemistry and Biochemistry
DETECTION OF TOXIC AGENTS IN WATER SYSTEMS
J. (ART) JANATA
School of Chemistry and Biochemistry
Georgia Institute of Technology
Phone:
OUTLINE
• OVERVIEW OF SENSORS/SYSTEMS - BASICS
• CHARACTERISTICS OF THE APPLICATION
• CONCLUSIONS
Workshop: “NEW TECHNOLOGIES”, Newark, June 27-28,2002
THIS PRESENTATION OUTLINES THE PROPERTIES OF SENSORS THAT ARE RELEVANT TO THE TASK OF PROTECTING DRINKING WATER SUPPLIES AGAINST INTENTIONAL OR UNINTENTIONAL CONTAMINATION.

2. SENSORS ARE DIFFERENT THAN
SENSING SYSTEMS
• SENSORS ACQUIRE INFORMATION CONTINUOUSLY
• SENSING SYSTEMS (ASSAYS) ARE DISCONTINUOUS,
CONTAIN DISCRETE STEPS
THERE IS A FUNDAMENTAL DIFFERENCE BETWEEN SENSORS AND SENSING SYSTEMS (ASSAYS). THE FORMER ACQUIRE INFORMATION CONTINUOUSLY WHILE THE LATTER DO IT DISCRETELY, IN SERIES OF STEPS. THE TWO APPROACHES ARE COMPLEMENTARY. THE CHOICE OF ONE OVER THE OTHER IS ALWAYS DICTATED BY THE APPLICATION.

3. THE SIGNAL IN CHEMICAL SENSORS ARISES FROM THE INTERACTION OF THE ANALYTE WITH THE SELECTIVE LAYER. THIS INTERACTION CAN OCCUR EITHER IN THE BULK OF THE LAYER OR AT ITS SURFACE. INVARIABLY, IT NEEDS TO BE AMPLIFIED. THERE ARE FOUR GROUPS OF AMPLIFICATION MECHANISMS USED IN CHEMICAL SENSORS

4. SENSOR BASICS RESPONSE CONCENTRATION SATURATION DYNAMIC RANGE
SENSITIVITY
INTERFERENCES
RESPONSE
CONCENTRATION
DETECTION LIMIT
THE RESPONSE CURVE OF THE SENSOR HAS COMMON IMPORTANT CHARACTERISTICS. THE RANGE OF CNCENTRATIONS IN WHICH THE SENSOR RESPONDS IS CALLED DYNAMIC RANGE. IT IS BOUND ON ITS UPPER END BY THE SATURATION LIMIT AND ON ITS LOWER END BY THE DETECTION LIMIT. INCREASING AMOUNT OF INTERFERING COMPOUNDS SHIFTS THE DETECTION LIMIT TO HIGHER CONCENTRATIONS THUS REDUCING THE DYNAMIC RANGE. SENSITIVITY IS THE SLOPE OF THE RESPONSE CURVE IN THE DYNAMIC RANGE.

5. t tdel t63% RESPONSE TIME > minutes for bulk
GENERAL LIMITATIONS OF CONTINUOUS OPERATION
• BASELINE STABILITY
• LOSS OF SENSITIVITY
• POWER CONSUMPTION
t63%
TIME
RESPONSE
63%
tdel
RESPONSE TIME IS ANOTHER FIGURE OF MERIT THAT DESCRIBES THE DYNAMIC CHARACTERISTICS OF THE SENSOR. FOR EXPONENTIALLY RESPONDING SENSORS IT IS THE TIME WHEN THE SIGNAL REACHES THE 63%OF ITS MAXIMUM VALUE. FOR NON-EXPONENTIAL SENSORS IT CAN BE CHOSEN ARBITRARILY AS E.G. 95% OR 99% OF THE MAXIMUM VALUE.
> minutes for bulk
< seconds for surface t

6. BIOSENSING SYSTEM (ASSAY)
SAMPLE
REAGENT
ADDITION
INCUBATION
MEASUREMENT
INTRODUCTION
DISCRETE STEPS
SENSING SYSTEMS OPERATE IN SEQUENCE OF STEPS. THE ANALYTICAL INFORMATIONIS ACQUIRED WITH CERTAIN INFORMATION ACQUISITION FREQUENCY. IN SLOWLY CHANGING SAMPLES SENSING SYSTEMS MAY BE PREFERABLE BECAUSE THEY ALLOW FOR INTERMITTENT CALIBRATION TO BE PERFORMED. MOST “BIOSENSORS” DISCUSSED IN THE LITERATURE ARE IN REALITY “BIOSENSING SYSTEMS”.
EVALUATION
READOUT
INFORMATION
CALIBRATION POINT
TIME

7. Revolutionary Advance in Laboratory Technology
Solution: Lab-on-a-Chip Technology
Revolutionary Advance in Laboratory Technology
Miniaturization, Integration, Automation
The Lab-on-a-Chip accomplishes life sciences data acquisition using a novel paradigm of integration: miniature, automated data is generated by processing a large portion of the protocol on the same device, rather than shuttling test tubes or multiwell plates from one single function device to the next.

8. An integrated microfluidic device
Nanoliter internal volumes, channel cross-sections in the 10 to 100 µm range (needed for fast diffusion times)
Electrokinetic movement of liquids and samples (allows for control at many wells)
PHOTOGRAPH OF A TYPICAL MICROFLUIDIC BIOSENSING SYSTEM (Courtesy of Caliper Inc.). NOTE THAT THE VOLUME OF THE LIQUID HANDLED BY THIS CHIP IS IN NANOLITERS

9. Personal Laboratory Workstation
PHOTOGHRAPH OF CALIPER BYOSENSING SYSTEM (Courtesy of Caliper Inc.)

10. The Microfluidic Toolbox
1 Separations: DNA, RNA, Proteins
2 Enzyme Activity Assays
3 Joule Heating on a Chip
4 PCR on a Chip
5 Solid Phase Reagent Storage
6 Cell and Bead Assays
7 Viscometer
8 Sample Preparation
AN EXAMPLE OF TYPES OF BIOASSAYS PERFOMED BY THE CALIPER SYSTEM

11. FLOW INJECTION ANALYSIS IS ANOTHER SENSING SYSTEM ARRANGEMENT
FLOW INJECTION ANALYSIS IS ANOTHER SENSING SYSTEM ARRANGEMENT. IT OPERATES WITH MICROLITER SAMPLES. PRACTICALLY ALL WET-ANALYTICAL PROCEDURES HAVE BEEN PERFORMED IN THE FIA FORMAT. IT IS FULLY MODULAR.

12. FIELD-DEPLOYABLE SYSTEM FOR Cr(VI) ANALYSIS
Sample Size:
< 500 microliters
50 microliters analyzed
< 2 minutes per sample
total volume of waste
1.5 milliliters per sample
10 ppb to 5 ppm range
EXAMPLE OF FIA ANALYSIS FOR Cr(VI) IN ENVIRONMENTAL SAMPLES PERFORMED IN “SEQUENTIAL FLOW ANALYSIS MODE”

13. CHARACTERISTICS OF DETECTION
IN WATER SYSTEMS
• LARGE SAMPLE VOLUME
• DILUTION
• LONG TIME CONSTANT
• WATER AS A MEDIUM
• HYDROLYSIS
• BIOLOGICAL AGENTS
• LIMITED ACCESIBILITY OF WATER TOWERS
• EASY ACCESS TO RESERVOIRS
THE CHOICE OF THE DIRECT SENSORS OR SENSING SYSTEMS IS DICTATED BY THE CHARACTERISTICS OF THE APPLICATION. FOR WATER ANALYSISSENSING SYSTEMS WOULD BE A BETTER CHOICE BECAUSE OF THE LARGE AVAILABLE SAMPLE VOLUMES, REQUIREMENT OF LONG TERM STABILITY OF THE BASELINE, USUALLY AVAILABLE SPACE. WATER AS THE ANALYTICAL MEDIUM IS A PREREQUISITE FOR MOST BIOASSAYS.

14. TOXICITIES OF LETHAL GASES
HERE IS AN EXAMPLE HOW THE POTENCY OF A TOXIC COMPOUND CHANGES WITH THE MODE OF ITS DEPLOYMENT. THIS EXAMPLE IS TAKEN FROM THE APPLICATION OF TOXIC GASES.

15. TOXICITY OF VARIOUS COMPOUNDS IS EXPRESSED ON LOG SCALE, RELATIVE TO CHLORINE WHICH IS TAKEN AS ONE

16. IF THE TOXIC GAS IS APPLIED FROM THE TOP ITS TOXICITY MUST BE MULTIPLIED BY ITS RELATIVE DENSITY WITH RESPECT TO AIR. THAT YIELDS ITS “POTENCY” FOR THIS FORM OF DEPLYOMENT

17. THE SAME GROUP OF COMPOUNDS RELEASED FROM THE “BOTTOM UP” HAVE A POTENCY DETERMINED BY THEIR VOLATILITY

18. HARMFUL AGENTS DETECTION • INORGANIC POISONS: HEAVY METALS; CYANIDE...
• INFECTIOUS BACTERIAL/VIRAL AGENTS
• TOXINS: AFLATOXINS, RICINE, ANTHRAX,...
• RADIONUCLIDES: Cs-137; Sr-90; Tc-99m; Np-237,...
HARMFUL AGENTS TO WORRY ABOUT WITH RESPECT TO THE WATER SUPPLY
DETECTION
• ASSAYS
• RADIATION DETECTORS

19. IMPORTANT DIFFERENCES BETWEEN DETECTION
OF THREAT AGENTS IN AIR AND IN WATER
GAS WATER
REQUIRED RESPONSE TIME SHORT LONG
BIOAGENTS DIFFICULT EASY
DISTRIBUTION PATTERNS COMPLEX PREDICTABLE
REMEDIAL ACTION COMPLEX SIMPLE
MODES OF ATTACK MANY FEW
AVAILABLE SPACE LIMITED AMPLE
IMPACT LIMITED LARGE
IN THIS VUGRAPH IMPORTANT DIFFERENCES BETWEEN DETECTION IN WATER IND IN AIR ARE OUTLINED

20. CONCLUSIONS (PROTECTION OF WATER SYSTEMS)
PROTECTION OF CLOSED SPACES OR WATER SUPPLIES HAS TO BE DESIGNED WITH SPECIFIC CHARACTERISTICS OF EACH SIUATION IN MIND. THIS CONCLUSION HAS BEEN REACHED AT THE NSF-SPONSORED WORKSHOP HELD IN JANUARY 2002.
NSF Workshop: “New Challenges in Chemical and Biosensing”, January 9-10, 2002