Systems and methods for rapidly changing the solution environment around sensors

Abstract

The invention provides microfluidic systems for altering the solution environment around a nanoscopic or microscopic object, such as a sensor, and methods for using the same. The invention can be applied in any sensor technology in which the sensing element needs to be exposed rapidly, sequentially, and controllably, to a large number of different solution environments whose characteristics may be known or unknown.

1 . A system, comprising: 
 a substrate for changing a solution environment around a sensor, the substrate comprising a plurality of channels, each channel comprising an outlet; and    a scanning mechanism for selectively exposing a sensor to a fluid stream from an outlet.    
     
     
         2 . A system comprising a substrate for changing a solution environment around a sensor, the substrate comprising: 
 an open-volume chamber for receiving a sensor; and    a plurality of channels, each channel comprising an outlet for delivering a substantially separate fluid stream into the chamber.    
     
     
         3 . A system, comprising: 
 a substrate for changing a solution environment around a sensor, the substrate comprising a plurality of channels, each channel comprising an outlet for delivering a substantially separate fluid stream to a sensor; and    a processor for controlling delivery of fluid from each channel to the sensor.    
     
     
         4 . The system of  claim 2 , wherein the chamber is capable of delivering an electrical current to a sensor placed within the chamber.  
     
     
         5 . The system of any of claims  1 - 3 , wherein at least one channel is in communication with a reservoir.  
     
     
         6 . The system of  claim 5 , wherein the reservoir is a buffer reservoir.  
     
     
         7 . The system of  claim 5 , wherein the reservoir is a sample reservoir.  
     
     
         8 . The system of  claim 5 , comprising a plurality of buffer reservoirs and sample reservoirs.  
     
     
         9 . The system of  claim 7 , wherein the each reservoir is in communication with a different channel.  
     
     
         10 . The system of  claim 9 , comprising alternating sample and buffer reservoirs.  
     
     
         11 . The system of  claim 5 , further comprising a mechanism for applying positive or negative pressure to the reservoir.  
     
     
         12 . The system of  claim 1 , wherein the scanning mechanism comprises a mechanism for moving the sensor in proximity to an outlet.  
     
     
         13 . The system according to  claim 1 , wherein the scanning mechanism comprises a mechanism for varying pressure across one or more channels.  
     
     
         14 . The system of  claim 2  further comprising at least one drain channel communicating with the chamber.  
     
     
         15 . The system of any of claims  1 - 3 , wherein the system further comprises a mechanism for holding a sensor which is coupled or connected to a positioner for positioning the sensor in proximity to an outlet of a channel.  
     
     
         16 . The system of  claim 15 , further comprising a capillary which is in sufficient proximity to the mechanism for holding the sensor, or which can be moved in sufficient proximity to the mechanism for holding the sensor, wherein the capillary is capable of delivering a fluid to a sensor positioned by the positioner.  
     
     
         17 . The system of  claim 15  or  16 , wherein the mechanism for holding the sensor comprises a mechanism for holding a cell.  
     
     
         18 . The system of  claim 16 , wherein the fluid from the capillary is a buffer.  
     
     
         19 . The system of any of claims  1 - 3 , further comprising a sensor.  
     
     
         20 . The system of  claim 19 , wherein the sensor comprises a cell or a portion of a cell.  
     
     
         21 . The system of  claim 20 , wherein the cell is a patch clamped cell or patch-clamped cell membrane fraction.  
     
     
         22 . The system of  claim 20 , wherein the cell or portion of the cell comprises an ion channel.  
     
     
         23 . The system of  claim 20 , wherein the cell or portion of the cell comprises a G Protein Coupled Receptor.  
     
     
         24 . The system according to  claim 20 , wherein the cell or portion of the cell comprises an activated receptor.  
     
     
         25 . The system of  claim 20 , wherein the cell or portion of a cell is selected from the group consisting of a cultured cell, a bacterial cell, a protist cell, a yeast cell, a plant cell, an insect cell, an avian cell, an amphibian cell, a fish cell, a mammalian cell, an oocyte, a cell expressing a recombinant nucleic acid, and a cell from a patient with a pathological condition.  
     
     
         26 . The system of  claim 20 , wherein the cell or portion of the cell is positioned in the in proximity to the outlet of a channel using a positioner.  
     
     
         27 . The system of any of claims  1 - 3 , wherein the system further comprises a sensor, and wherein the sensor is selected from the group consisting of: a surface plasmon energy sensor; an FET sensor; an ISFET; an electrochemical sensor; an optical sensor; an acoustic wave biosensor; a sensor comprising a sensing element associated with a Quantum Dot particle; a polymer-based biosensor; and an array of biomolecules immobilized on a substrate.  
     
     
         28 . The system of any of claims  1 - 3 , wherein the system comprises a plurality of sensors.  
     
     
         29 . The system of any of claims  1 - 3 , wherein each fluid stream of the plurality of channels is substantially parallel.  
     
     
         30 . The system of  claim 2 , wherein at least a portion of the chamber is optically transmissive.  
     
     
         31 . The system of  claim 2  wherein the chamber comprises a plurality of wells, each well for receiving a cell.  
     
     
         32 . The system of  claim 2 , wherein the chamber comprises at least one electrical element for changing electrical properties of a solution in the chamber.  
     
     
         33 . The system of any of  claim 31 , wherein each well comprises an electrical element for making an electrical contact with a cell.  
     
     
         34 . The system of  claim 31 , further comprising a mechanism for varying pressure across one or more channels in the substrate for selectively exposing a cell in a well to a fluid stream from a selected channel.  
     
     
         35 . The system of any of claims  1 - 3 , wherein the diameter of each channel outlet is at least about the diameter of the sensor.  
     
     
         36 . The system of  claim 35 , wherein the sensor comprises a cell.  
     
     
         37 . The system of any of claims  1 - 3 , wherein each channel comprises at least one inlet for receiving solution from a reservoir, and wherein the center-to center distance of each reservoir corresponds to the center-to-center distance of wells in a multi-well plate.  
     
     
         38 . The system of any of claims  1 - 3 , wherein the substrate further comprises one or more treatment chambers for delivering an electrical current to a cell placed within the treatment chamber.  
     
     
         39 . The system of  claim 15 , wherein the mechanism for holding the sensor is selected from the group consisting of a pipette or a capillary connected to a positioner, and an optical tweezer.  
     
     
         40 . The system of  claim 16 , wherein the mechanism for holding the sensor is a pipette and the capillary is coaxial with the p pipette.  
     
     
         41 . The system of  claim 39 , wherein the pipette is a patch clamp pipette.  
     
     
         42 . The system of  claim 15 , wherein the mechanism for holding the sensor comprises an electrode.  
     
     
         43 . The system of  claim 2  or  3 , further comprising a scanning mechanism for selectively exposing a sensor to a fluid stream from an outlet.  
     
     
         44 . The system of  claim 43 , wherein the scanning mechanism comprises a mechanism for scanning the sensor across the plurality of channel outlets.  
     
     
         45 . The system of  claim 43 , wherein the scanning mechanism comprises a mechanism for varying pressure across one or more channels in the substrate.  
     
     
         46 . The system of  claim 1 , wherein the scanning mechanism is capable of moving the substrate or the sensor, or both the substrate and the sensor.  
     
     
         47 . The system of  claim 43 , wherein when the scanning mechanism is capable of moving the substrate and the sensor, the sensor and substrate are capable of moving independently of each other.  
     
     
         48 . The system of  claim 43 , wherein movement of the sensor or substrate or both the sensor and substrate, occurs upon a predefined response of the sensor to fluid from a channel outlet.  
     
     
         49 . The system of  claim 1 , further comprising a processor in communication with the scanning mechanism.  
     
     
         50 . The system of  claim 43 , further comprising a processor in communication with the scanning mechanism.  
     
     
         51 . The system of  claim 1 , wherein the processor controls one or more of: the rate of scanning, the direction of scanning, acceleration of scanning, number of scans, pause intervals at a channel and pressure changes across one or more channels.  
     
     
         52 . The system of  claim 43 , wherein the processor controls one or more of: the rate of scanning, the direction of scanning, acceleration of scanning, number of scans, pause intervals at a channel, and pressure changes across one or more channels.  
     
     
         53 . The system of any of claims  1 - 3 , further comprising a detector in communication with the sensor for detecting the responses of a sensor in the chamber.  
     
     
         54 . The system of  claim 53 , wherein the detector communicates with a processor comprising a data acquisition system.  
     
     
         55 . The system of  claim 49 , wherein the processor further comprises or communicates with a data analysis system.  
     
     
         56 . The system of  claim 53 , wherein the processor communicates with a user interface for displaying data related to the responses.  
     
     
         57 . The system of  claim 56 , wherein the user interface is a computer or a wireless device.  
     
     
         58 . The system of  claim 49 , wherein in response to a signal from the detector, the processor alters one or more of the rate of scanning, the direction of scanning, acceleration of scanning, number of scans, and pressure changes across one or more channels.  
     
     
         59 . The system of  claim 1  or  3 , wherein at least one channel outlet opens into a chamber for receiving the sensor.  
     
     
         60 . The system of  claim 2 , wherein each of the channels simultaneously delivers a fluid stream into the open volume chamber.  
     
     
         61 . The system of  claim 60 , wherein each of the channels simultaneously delivers a fluid stream into the open volume chamber.  
     
     
         62 . The system of  claim 5 , wherein the system is interfaced to a fluid delivery system operably linked to a micropump for pumping fluids from the fluid delivery system into one or more reservoirs of the substrate.  
     
     
         63 . The system of  claim 62 , wherein the fluid delivery system comprises one or more microtiter plates.  
     
     
         64 . The system of  claim 62 , wherein the fluid delivery system is capable of programmably delivering different types of samples and/or buffer to the one or more reservoirs.  
     
     
         65 . The system of  claim 62 , wherein the fluid delivery system is capable of programmably delivering buffer to at least one reservoir.  
     
     
         66 . The system of  claim 10 , wherein the system delivers streams of sample and buffer through interdigitated channels of the substrate.  
     
     
         67 . The system of  claim 20 , wherein the cell comprises a receptor and the system delivers a buffer; at least one agonist; at least one agonist and a buffer; at least one antagonist; or at least one antagonist and a buffer through channels of the substrate.  
     
     
         68 . The system of  claim 20  or  claim 67 , wherein the system comprises a chamber for receiving the cell or portion thereof which is in communication with the channels and wherein the chamber comprises a buffer, at least one agonist; at least one agonist and a buffer; at least one antagonist; at least one antagonist and a buffer; or at least one antagonist, at least one agonist, and a buffer.  
     
     
         69 . The system of  claim 67 , wherein the at least one agonist and buffer; the at least one antagonist and buffer; or the at least one antagonist, at least one agonist, and buffer, are delivered to the cell through interdigitated channels of the substrate.  
     
     
         70 . The system of any of claims  1 - 3 , further comprising at least one output channel for removing fluid from the system.  
     
     
         71 . The system of any of claims  1 - 3 , further comprising a mechanism for delivering positive or negative pressure to at least one of the channels.  
     
     
         72 . The system of  claim 71 , wherein the mechanism for delivering pressure is in communication with a processor.  
     
     
         73 . The system of  claim 72 , wherein the processor provides instructions to the mechanism for delivering pressure to one or more selected channels.  
     
     
         74 . The system of any of claims  1 - 3 , wherein the substrate is interfaced with a multi-well plate and wherein each well is in fluid communication with a different channel on the substrate.  
     
     
         75 . The system of  claim 74 , wherein wells communicate with the channels through one or more external tubings or capillaries for delivering to the fluid to the channels.  
     
     
         76 . The system of  claim 74 , wherein the one or more tubings or capillaries comprise one or more external valves to control fluid flow through the tubings or capillaries.  
     
     
         77 . The system of  claim 5 , wherein at least one reservoir is sealed by a septum.  
     
     
         78 . The system of  claim 74 , wherein a tube or needle is inserted into the septum.  
     
     
         79 . The system of  claim 16 , wherein the capillary is coupled to a pumping mechanism to provide pulsatile delivery of buffer to the sensor.  
     
     
         80 . The system of any of claims  1 - 3 , wherein the substrate comprises a material selected from the group consisting of a crystalline semiconductor material; silicon; silicon nitride; Ge, GaAs; metals; Al, Ni; glass; quartz; crystalline insulator; ceramics; plastics; an elastomeric material; silicone; EPDM; Hostaflon; a polymer; a fluoropolymer; Teflon®; polymethylmethacrylate; polydimethylsiloxane; polyethylene; polypropylene; polybutylene; polymethylpentene; polystyrene; polyurethane; polyvinyl chloride; polyarylate; polyarylsulfone; polycaprolactone; polyestercarbonate; polyimide; polyketone; polyphenylsulfone; polyphthalamide; polysulfone; polyamide; polyester; epoxy polymer; thermoplastic; an organic material; an inorganic material; combinations thereof.  
     
     
         81 . The system of any of claims  1 - 3 , wherein the substrate is three-dimensional and at least two of the channels lie at least partially in different planes.  
     
     
         82 . The system of  claim 81  comprising a first set of channels and a second set of channels and wherein the first set of channels overlies the second set of channels.  
     
     
         83 . The system of any of claims  1 - 3 , wherein at least one channel is a mixing channel for combining fluid streams from at least two channels.  
     
     
         84 . The system of  claim 84 , wherein the mixing channel provides a fluid comprising a varying concentration of a substance.  
     
     
         85 . A method for generating an activated receptor, comprising 
 a) providing a substrate, the substrate comprising: 
 a chamber comprising a cell-based biosensor comprising a receptor which is activated by an agonist; and  
 a plurality of delivery channels delivering agonist, antagonist, or both agonist and antagonist, each channel comprising an outlet for delivering a substantially separate aqueous stream into the chamber; and  
   b) selectively exposing the biosensor to a fluid stream from one or more outlets.    
     
     
         86 . The method of  claim 85 , wherein the chamber comprises a buffer, at least one agonist, at least one antagonist, or a combination thereof.  
     
     
         87 . A method for detection of a modulator of a receptor, comprising 
 a) providing a substrate, the substrate comprising: 
 a chamber comprising a cell-based biosensor, the biosensor comprising the receptor; and  
 a plurality of channels, each channel comprising an outlet for delivering a substantially separate fluid stream into the chamber; and  
 a scanning mechanism for selectively exposing the biosensor to a fluid stream from one or more outlets,  
   b) providing a sample suspected of containing a modulator to at least one of the channels;    c) measuring the response of the biosensor as it is selectively exposed to a fluid stream comprising the sample, wherein a change in the response of the biosensor indicates the presence of a modulator in the sample.    
     
     
         88 . The method of  claim 85  or  87 , wherein the exposing step is performed by moving the substrate or the sensor or both the substrate and the sensor relative to at least one channel outlet.  
     
     
         89 . The method of  claim 88 , wherein both the substrate and sensor are moved independently of each other.  
     
     
         90 . The method of  claim 85  or  87 , wherein the exposing step further comprises producing pressure drops across one or more channels.  
     
     
         91 . The method of  claim 87 , wherein the same suspected modulator is provided to a plurality of channels.  
     
     
         92 . The method of  claim 87 , wherein different concentrations of the modulator are provided to the plurality of channels.  
     
     
         93 . The method of  claim 87 , wherein the modulator varies in concentration in at least one channel, forming a gradient of modulator in the at least one channel.  
     
     
         94 . The method of  claim 87 , further comprising generating a dose-response curve for the modulator.  
     
     
         95 . The method of  claim 87 , comprising exposing the biosensor to buffer delivered by at least one channel.  
     
     
         96 . The method of  claim 95 , comprising selectively exposing the biosensor to streams of buffer and sample.  
     
     
         97 . The method of  claim 96 , comprising selectively exposing the biosensor to alternating streams of buffer and sample.  
     
     
         98 . The method of  claim 85  or  87 , wherein the cell-based biosensor comprises a patch-clamped cell or patch-clamped cell membrane fraction.  
     
     
         99 . The method of  claim 98 , wherein the patch-clamped cell is positioned relative to the outlets using a patch clamp pipette coupled or connected to a positioner.  
     
     
         100 . The method of  claim 98 , wherein the patch-clamped cell or patch-clamped cell membrane fraction is positioned in a depression in the base of the chamber.  
     
     
         101 . The method of  claim 87 , wherein the receptor is activated by an agonist which produces a measurable response by the biosensor upon binding to the receptor, and wherein the modulator modulates the activity of the agonist.  
     
     
         102 . The method of  claim 87 , wherein the receptor is inactivated by an antagonist which eliminates or reduces a measurable response by the biosensor upon binding to the receptor, and wherein the modulator modulates the activity of the antagonist.  
     
     
         103 . The method of  claim 87 , wherein the modulator is an agonist.  
     
     
         104 . The method of  claim 87 , wherein the modulator is an antagonist.  
     
     
         105 . The method of 87, wherein the channels deliver a buffer, at least one agonist; at least one antagonist; at least one agonist and a buffer; at least one antagonist and a buffer; or at least one antagonist, at least one agonist, and a buffer.  
     
     
         106 . The method of  claim 87  or  105 , wherein the chamber comprises a buffer, at least one agonist, or at least one antagonist.  
     
     
         107 . The method of  claim 85  or  87 , wherein the cell-based biosensor comprises an ion-channel.  
     
     
         108 . The method of  claim 85  or  87 , wherein the receptor comprises a G-protein coupled receptor.  
     
     
         109 . The method of  claim 85  or  87 , wherein the cell-based biosensor comprises a recombinantly expressed receptor.  
     
     
         110 . The method of  claim 109 , wherein the recombinantly expressed receptor is an orphan receptor.  
     
     
         111 . The method of  claim 87 , wherein the response is determined by measuring cell surface area.  
     
     
         112 . The method of  claim 87 , wherein the response is determined by measuring an electrical property of the cell-based biosensor.  
     
     
         113 . The method of  claim 87 , wherein the modulator is a modulator of neurotransmitter release.  
     
     
         114 . The method of  claim 87 , wherein the response is determined by measuring ion-channel permeability properties.  
     
     
         115 . A method for changing a solution environment locally around a nanoscopic or microscopic object, comprising: 
 (a) providing a substrate, comprising: 
 a chamber comprising the nanoscopic or microscopic object and a fluid; and  
 a plurality of channels, each channel comprising an outlet intersecting with the chamber;  
   (b) delivering substantially separate streams of fluid into the chamber, at least two of the streams comprising different fluids;    (c) scanning the object sequentially across the at least two streams, thereby altering the aqueous solution environment around the object.    
     
     
         116 . The method of  claim 115 , wherein scanning is performed by moving the substrate, the object or both the substrate and the object.  
     
     
         117 . The method of  claim 115 , wherein scanning is performed by varying pressure across one or more channels.  
     
     
         118 . The method of  claim 115 , wherein the chamber comprises a plurality of nanoscopic or microscopic objects.  
     
     
         119 . The method of  claim 118 , wherein each object is scanned across at least two streams.  
     
     
         120 . The method of  claim 115 , wherein scanning is performed by a scanning mechanism controlled by a processor.  
     
     
         121 . The method of  claim 120 , where in the processor controls positioning of the object relative to the channels.  
     
     
         122 . The method of  claim 120 , wherein the processor controls a scanning parameter selected from the group consisting of: the direction of scanning, acceleration of scanning, number of scans, pause intervals at a channel and pressure changes across one or more channels.  
     
     
         123 . The method of  claim 122 , wherein a scanning parameter is modified by the processor in response to a feedback signal.  
     
     
         124 . The method of  claim 123 , wherein the feedback signal is a response of the object to one or more of the streams.  
     
     
         125 . The method of  claim 115 , wherein the substrate further comprises at least two channels comprising outlets intersecting with the chamber and wherein aqueous streams exiting from the at least two channels are collimated and laminar within a volume of fluid within the chamber.  
     
     
         126 . The method of  claim 79 ,  80 , or  105 , wherein hydrostatic pressure at each of the plurality of channels is different.  
     
     
         127 . The method of  claim 85  or  87 , or  115 , wherein the viscosity of fluids in at least two of the channels is different.  
     
     
         128 . The method of  claim 85  or  87 , or  105 , wherein each channel comprises fluid having a different viscosity.  
     
     
         129 . The method of  claim 85  or  87 , or  115 , wherein fluid within at least two of the channels are at a different temperature.  
     
     
         130 . The method of  claim 85  or  87 , or  115 , wherein the temperature of fluid in each of the channels is different.  
     
     
         131 . The method of  claim 85  or  87 , or  115 , where the osmolarity of fluid within at least two of the channels is different.  
     
     
         132 . The method of  claim 131 , wherein the osmolarity of fluid with each of the channels is different.  
     
     
         133 . The method of  claim 85  or  87 , or  105 , wherein the ionic strength of fluid within at least two of the channels is different.  
     
     
         134 . The method of 85 or 87, or 115, wherein the streams flowing in at least two channels flows at different velocities.  
     
     
         135 . The method of  claim 85  or  87 , or  115 , wherein fluid entering the chamber is withdrawn from the chamber.  
     
     
         136 . The method of  claim 135 , wherein fluid is withdrawn through the same channel through which it entered the chamber.  
     
     
         137 . The method of  claim 135 , wherein fluid is withdrawn through a different channel from the channel through which it entered the chamber.  
     
     
         138 . The method of  claim 115 , wherein the object is a sensor and the method further comprises measuring the response of the sensor to one or more fluid streams.  
     
     
         139 . The method of  claim 138 , wherein the sensor comprises a cell membrane and the method further comprises the step of exposing the cell membrane to an electric field.  
     
     
         140 . The method of  claim 139 , wherein the electric field induces pore formation in the cell membrane.  
     
     
         141 . The method of  claim 139 , wherein the response is determined by measuring ion currents.  
     
     
         142 . The method of  claim 139 , wherein the response is determined by measuring voltage.  
     
     
         143 . The method of  claim 139 , wherein the response is determined by measuring intracellular calcium.  
     
     
         144 . The method of  claim 139 , wherein the response is measured by measuring membrane stretching.  
     
     
         145 . The method of  claim 139 , wherein the response is the release of internal vesicles.  
     
     
         146 . The method of  claim 139 , wherein the response is the retrieval of vesicles by the membrane.  
     
     
         147 . The method of  claim 139 , wherein the object is stably associated with the base of the chamber.  
     
     
         148 . The method of  claim 85  or  87 , or  115 , wherein a fluid in at least one of the channels is delivered to the chamber by electrophoresis.  
     
     
         149 . The method of  claim 85  or  87 , or  115 , wherein a fluid in at least one of the channels is delivered to the chamber by pumping.  
     
     
         150 . The method of  claim 85  or  87  or  115 , wherein the method further comprises continuously or intermittently exposing the object to light of different wavelength.  
     
     
         151 . The method of  claim 115 , wherein the object is a micro- or nano-electrode.  
     
     
         152 . The method of  claim 115 , wherein the object selected from the group consisting of: a surface plasmon energy sensor; an FET sensor; an ISFET; an electrochemical sensor; an optical sensor; an acoustic wave biosensor; a sensor comprising a sensing element associated with a Quantum Dot particle; a polymer-based biosensor; and an array of biomolecules immobilized on a substrate.  
     
     
         153 . The method of  claim 115 , wherein the object is selected from the group consisting of: a eucaryotic cell, procaryotic cell, cell nucleus, infected cell, transfected cell, bacteria, organelle, organelle analog, gamete, electroporated cell, synaptosome, proteoliposome, liposomes and combinations thereof.  
     
     
         154 . The method of  claim 115 , further comprising continuously or intermittently superfusing the object with liquid from a fluid source at a rate higher or lower than the flow rate of the fluid in the channels.  
     
     
         155 . The method of  claim 115 , wherein the object is a cell, and the surface of the cell is continuously or intermittently superfused to resensitize an ion channel and/or receptor.  
     
     
         156 . The method of  claim 115 , wherein the object is a cell, and the surface of the cell is continuously or intermittently superfused to desensitize an ion channel and/or receptor.  
     
     
         157 . The method of  claim 115 , wherein the object is a cell, and the surface of the cell is continuously or intermittently superfused with liquid to block ion channels and/or receptors.  
     
     
         158 . The method of  claim 115 , wherein one more micro- or nanoelectrodes are placed close to the object.  
     
     
         159 . The method of  claim 158 , wherein the one more micro- or nanoelectrodes are used to continuously or intermittently expose the object to an electric field.  
     
     
         160 . The method of  claim 159 , wherein the exposing causes an electrochemical change in the nanoscopic or microscopic object.  
     
     
         161 . The method of  claim 160 , wherein the electrochemical change is oxidation or reduction.  
     
     
         162 . The method of  claim 115 , wherein the chamber comprises a plurality of wells, each well for receiving a cell.  
     
     
         163 . The method of  claim 162 , wherein each well comprises an electrical element for making electrical contact with the cell.  
     
     
         164 . The method of  claim 115 , further comprising transporting a microscopic or nanoscopic object through at least one channel into the chamber.  
     
     
         165 . The method according to  claim 115 , wherein one or more agents are delivered through the plurality of channels.  
     
     
         166 . The method according to  claim 115 , wherein the object is exposed to interdigitating agent and buffer streams.  
     
     
         167 . The method of  claim 165 , wherein the agent is selected from the group consisting of a candidate drug; a known drug; a suspected carcinogen; a known carcinogen; a candidate toxic agent, a known toxic agent; and an agent that acts directly or indirectly on ion channels.  
     
     
         168 . The method of  claim 115 , wherein the object is a cell and wherein a response of the cell to a fluid stream is used to monitor changes in a physiological response of the cell.  
     
     
         169 . The method of  claim 115 , wherein the physiological response is an abnormal physiological response associated with a disease state.  
     
     
         170 . The method of  claim 115 , wherein the substrate is implanted in the body of an organism.