Materials Day Agenda 2010

Biologics are the fastest growing sector of the pharmaceutical industry with significant growth projected for the next 10 years.  Inefficient pharmaceutical manufacturing processes however, have created an unnecessary burden on the U.S. healthcare system.  A recent study estimates that the pharmaceutical industry could be wasting more than $50 billion a year in manufacturing costs. The FDA has encouraged the Biopharmaceutical industry to adopt quality-by-design (QbD) manufacturing principles and Process Analytical Technologies (PAT) through its PAT Initiative.  The FDA defines PAT as:  “a system for designing, analyzing, and controlling manufacturing through timely measurements (i.e., during processing) of critical quality and performance attributes of raw and in-process materials and processes with the goal of ensuring final product quality.”

The development of platforms for conducting controlled, high-throughput, multiplexed experiments—a central focus of this proposal—will have a direct impact on cell line development, process optimization, and process validation.  The importance of high quality data and improved understanding of bioprocesses will increase as regulatory requirements evolve for this maturing industry and such knowledge should deepen insights into how the biology of production hosts and process variation affects the quality of protein therapeutics.  This talk will review the sensor needs and recent technology advances that allow for real-time in situ measurement of environmental parameters, cell concentration and viability, and medium components.

Today, reservoir characterization is mostly performed using a suite of tools deployed in the wellbore for measurements of formation resistivity, density, pressure, temperature, fluid type and other properties.  On-going efforts to miniaturize and manufacture robust and low-cost sensors are motivated by potential advances towards real-time reservoir measurements as well as multi-functional distributed micro/nano-scale sensor arrays for permanent monitoring applications.  Micro-electromechanical systems (MEMS) manufacturing techniques from the semiconductor industry are often applied, although many of the thin film materials used are not inherently designed to withstand harsh oilfield conditions. This often leads to the need to protect fragile sensing elements from direct contact with corrosive fluids, or preferably, to use sensor materials which are both mechanically robust and chemically inert.

In this talk, some of the challenges in reservoir characterization will be outlined, which include measuring reservoir properties beyond the wellbore, determining 3-D distribution of reservoir fluids and rocks, and the dynamic paths of reservoir fluids.  For wellbore measurements, an example of a silicon-based MEMS sensor that we have previously developed for downhole pressure and temperature measurements will be described.  For fluid studies in confined geometries, examples of our collaborative efforts in developing micro/nano-scale probes will be discussed, which include a carbon-nanotube based probe to study ionic and fluidic transport [1], as well as integrated Fresnel zone plates to characterize fluid behavior within a microfluidic channel [2].

[1] B. Bourlon, J. Wong, C. Miko, L. Forro, M. Bockrath, “A nanoscale probe for fluidic and ionic transport,” Nature Nanotech., 2, 104-107 (2007).
[2] E. Schonbrun, J. Wong, K. B. Crozier, “Co- and cross-flow extensions in an elliptical optical trap,” Phys. Rev. E, 79, 042401 (2009).

Organic electronic materials display a diversity of function and performance unmatched by conventional electronic materials. Optimal implementation requires sophisticated molecular designs and complex syntheses, which are often lacking in sensory materials. I will discuss our efforts to create new generations of materials based upon carbon nanotubes.  Chemical functionalizations have been developed to create materials that exhibit specific resistive changes to target analytes.  The advantages of chemiresistive sensors include the following:  (1) Small changes in resistance can be measured with high precision and inexpensive electronics.  (2) Resistivity sensors have very low power requirements.  (3) Resistive materials are readily integrated into many different structures, ranging from integrated circuits to fabrics.  (4) The simplicity of a resistive measurement is ideal for the formation of cross-reactive array (e-nose or e-tongue) devices.

Restricted geometries created by nanostructures will be used to impart superior sensitivity to chemical sensors.  The obvious advantage in these types of systems is increased interfacial area to interact with the analytes, however for chemiresistors these systems can realize much larger gains. Conducting polymer-carbon nanotubes (CNTs) composites can create sensory devices with finite numbers of conduction pathways. For single-walled CNTs (SWCNTs), analyte induced resistance changes occur along the length of the nanotube as well as at the junctions. An impressive illustration of the selectivity possible involves wrapping SWCNTs with a conducting polymer containing calix[4]arene receptors. SWCNTs are naturally p-doped generally responsive to chemicals with oxidizing/reducing/polar characteristics and these factors can yield selective responses. However, we have succeeded in generating selective CNT sensors with differential responses to non-polar o-, m-, and p-xyelene. In addition to chemical sensors, we will present recent results on the use of carbon nanotube materials for the detection of ionizing radiation (Figure 1) and DNA.

Nanotechnology is having a transformative impact on sensor technology, particularly with the emergence of transducers and detectors capable of sensing the adsorption and desorption of single molecules.  Such sensor platforms yield unprecedented molecular discrimination and analysis of complex mixtures, and are spawning a new generation of biological and single cell assays.  Such stochastic sensors require new thinking in how to multiplex and handle the data streams that emerge from nanosensor arrays to extract useful information in space and time.  This presentation will review the scientific and technological developments that provide the foundation for this emerging area.  Two recent examples from the Strano laboratory at MIT are discussed.  In the first¹, fluorescent single walled carbon nanotubes can be used to selectively detect single molecules of reactive oxygen and reactive nitrogen species such as H₂O₂ and NO, even from the efflux of single biological cells.  We used this platform to study an important problem related to cell signaling.   An emerging concept in cell signalling is the natural role of reactive oxygen species such as hydrogen peroxide (H2O2) as beneficial messengers in redox signalling pathways. In spite of the growing evidence, the nature of H2O2 signalling is confounded by difficulties in tracking it in living systems, both spatially and temporally, at low concentrations. An array of fluorescent single-walled carbon nanotubes can selectively record, in real time, the discrete, stochastic quenching events that occur as H2O2 molecules are emitted from individual human epidermal carcinoma cells stimulated by epidermal growth factor. We show mathematically that such arrays can distinguish between molecules originating locally on the cell membrane from other contributions.  The platform promises a new approach to understanding the signalling of reactive oxygen species at the cellular level.  In a second example², the nanotube interior is used as a single molecule conduit and sensor.  Biological signaling networks are able to utilize coherent and oscillatory signals from intrinsically noisy and stochastic components for ultrasensitive discrimination using stochastic resonance, a concept not yet demonstrated in man-made analogs.  We show that the longest, highest aspect ratio, and smallest diameter synthetic nanopore examined to date, a 500 μm single walled carbon nanotube (SWNT), approximately 1.5 nm in diameter, demonstrates oscillations in electro-osmotic current at specific ranges of electric field, that are the signatures of stochastic resonance, yielding rhythmic and frequency locked signals.  SWNT were grown on a SiO₂ wafer and connected between two bonded, aqueous reservoirs at their plasma-etched and open ends.  Stochastic pore blocking is observed when individual cations (Na⁺, Li⁺, K⁺, 1 M) partition into the nanotube during electro-osmosis, partially obstructing an otherwise stable proton current.  We report the highest recorded proton conductivity experimentally observed (5×10² S/cm), suggesting an ordered water phase in the SWNT interior.  The observed oscillations in the current occur due to a coupling between stochastic pore blocking and a diffusion limitation that develops at the pore mouth during proton transport.  This is the first example of stochastic resonance in a synthetic nanopore, and illustrates how simple ionic transport can generate coherent waveforms within an inherently noisy environment, and points to new types of nano-reactors, sensors, and nanofluidic channels based on this platform.

1.     Jin H, Heller DA, Kalbacova M, Kim JH, Zhang JQ, Boghossian AA, Maheshri N, Strano MS: Detection of single-molecule H2O2 signalling from epidermal growth factor receptor using fluorescent single-walled carbon nanotubes. NATURE NANOTECHNOLOGY, 5 (2010), 302-309.

2.     Lee, C.Y, Choi W, Han, J.-H., Strano MS: Coherence Resonance in a Single-Walled Carbon Nanotube Ion Channel. SCIENCE, 239, 1320 - 1324 (2010).

T2Biosystems’s proprietary system combines magnetic resonance and nanotechnology in a device that for the first time enables nucleic acid, immunoassay, blood culture and coagulation testing on a single desktop instrument. Simple to operate, the technology is an ideal solution for use by unskilled users. T2Bio has productized the company’s proprietary detector and created robust, integrated benchtop detection units.  The company has developed a portfolio of assays that prove the ability of this platform to achieve central lab quality results across a wide range of analytes including sensitivities of ≤10 CFU/mL for pathogen detection directly in whole blood and femtomolar immunoassay sensitivity with CV’s as low as 5%.

The key advantage of the technology is that the T2 detection system does not require sample purification; thus, the skills, time-to-result, and cost associated with the analysis are greatly reduced. T2Bio’s proprietary integrated instrument will fully automate all assay processing steps after sample loading on a disposable cartridge. Further, the system is versatile enough to accommodate sample volumes from 1 uL to 4 mL or greater, and can detect in native biological fluids including blood, urine, and sputum. The platform has been used for detection of nucleic acids, metabolites, proteins, or small molecules within a single sample on the same instrument. Additionally, the technology is scalable to hand portable instruments and implantable, continuous monitoring applications.

We are currently developing a panel of whole-blood based immuno and nucleic acid tests for monitoring immunocompromised patients that provide rapid reference-lab-quality results with no sample preparation.

Medical technologies are evolving at a very rapid pace.  Portable communications devices and other handheld electronics are influencing our expectations of future medical tools.  The advanced medical technologies of our future will not necessarily be large expensive systems.  They are just as likely to be small and disposable.  This talk will review how Microsystems and microdevices are already impacting health care as commercial products or in clinical development.  Example systems include point of care diagnostics (POCT), patient monitoring tools, systemic drug delivery, local drug delivery, and surgical tools are described.  These technologies are moving care from hospitals to outpatient settings, the physician’s office, community health centers, nursing homes, and the patient’s home.

Adoption of new technologies depends greatly on compatibility with existing clinical practice.  Microsystems that are rapidly adopted fulfill significant medical needs and fit seamlessly with existing procedures. My group has been focusing on studying individual medical procedures and trying to make them do things never before thought possible or dramatically reduce morbidity associated with that procedure.

One example is the classic biopsy procedure.  Biopsies provide required information to diagnose cancer but, because of their invasiveness, they are difficult to use for managing cancer therapy. The ability to repeatedly sample the local environment for tumor biomarker, chemotherapeutic agent, and tumor metabolite concentrations could improve early detection of metastasis and personalized therapy. I will describe an implantable diagnostic device that senses the local in vivo environment. This device, which could be left behind during biopsy, uses a semi-permeable membrane to contain nanoparticle magnetic relaxation switches. These nanoparticles are engineered to aggregate in the presence of target biomarkers, which can be monitored non-invasively through magnetic resonance (MR) relaxometry.  A cell line secreting a model cancer biomarker produced ectopic tumors in mice. The transverse relaxation time (T₂) of devices in tumor-bearing mice was 26 ± 8 % lower than devices in control mice after one day by magnetic resonance imaging (p < 0.001). Short term applications for this device are numerous, including verification of successful tumor resection. I will describe this systems use for other molecular biomarkers and tumor metabolites.