Needle-type sensors

Some earlier developments and applications of various implantable pH sensors or measurement systems have been reported [128, 129, 130, 131]. However, reliable pH sensors for long-term implantations are still not available, and widespread clinical usage of implantable pH sensors has not been reached. Similar to other implantable sensors, the development of implantable pH microelectrodes, either fully implanted in the body or needle type sensors applied through the skin (percutaneous), has faced serious obstacles including sensor stability deterioration, corrosion, and adverse body reactions [48, 132, 133], Among them, encapsulation to prevent corrosion represents a major challenge for the implantable sensor devices [51]. Failure of encapsulation can cause corrosion damage on internal components, substrate materials, and electrical contacts [48], The dissolution of very thin pH sensitive layers will also limit the stability and lifetime of implantable micro pH sensors. 

Flow-Based Systems Needle-type sensors with a fluid flowing over the sensor tip seem to resist biofouling and extend sensor lifetime.31 There are numerous methods that have been investigated for flow-based sensors, such as microperfusion systems,75 microdialysis,76 77 and ultrafiltration.78 Reduced fouling was found with an open microflow system where slow flow of protein-free fluid over the sensor surface at the implant site is effected.73 Different from the other flow-based sensors, the open microflow is controlled by the subcutaneous tissue hydrostatic pressure and does not require a pump. 

Yang Q, Atanasov P, Wilkins E. A needle-type sensor for monitoring glucose in whole blood. Biomed Instrum Technol 1997 31 54-62. 

The second design is a needle-type sensor. Flere the enzyme is electrically deposited on the electrode surface using a conductive polymer. A conductive polymer is dissolved in phosphate buffer (we use phenylene diamine). To this solution the enzyme is added. The electrodes are dipped in the solution and a potential of +0.65 is applied for few seconds. The conductive polymer gets deposited along with the enzyme on the electrode surface. These electrodes are dipped in a solution, which is to be tested for the explosive. 

The electrochemical instrumentation used, fabrication of the needle-type sensor with an incorporated Ag/AgCl reference electrode, and electrodeposition of the PPD film have been described previously (14). Rotating disk studies of Nafion and PPD membranes were performed as described elsewhere (79). Nafion membrane thicknesses were determined using ellipsometry (79). Nafion and glucose oxidase membranes were cured for 1 h in an oven, or overnight at room temperature (75). 

Lee J-H, Seo Y, Lim T-S, Bishop PL, Papautsky 1 (2007) MEMS needle-type sensor array for in situ measurements of dissolved oxygen and redox potential. Environ Sci Technol 41 (22) 7857-7863. doi 10.1021/es070969o... 

D. Bindra, Y. Zhang, G. Wilson, R. Sternberg, D.Trevenot, G. Reach, and D. Moatti, Design and in vitro studies of a needle-type glucose sensor for subcutaneous monitoring. Anal. Chem. 63, 1692-1696 (1991). 

M. Shichiri, Y. Yamasaki, N. Hakui, and H. Abe, Wearable artificial endocrine pancreas with needle-type glucose sensor. Lancet 2, 1129-1131 (1982). 

Shichiri et al(ll) (Osaka University in Japan) has developed the micro needle type glucose sensor, which consisted of a hydrogen peroxide electrode and a GOX enzyme immobilized layer. The sensor was clinically used, but it had to be renewed after a few days because of a gradual decline in its output. 

Moussy F, Harrison DJ, O Brien DW, Rajette RV. Performance of subcutaneously implanted needle-type glucose sensors employing a novel trilayer coating. Analytical Chemistry 1993, 65, 2072-2077. 

Figure 4-17 Schematics of various implantable electrochemical/optical sensors useful for continuous in vivo monitoring (A) catheter style amperometric oxygen sensor (B) design of Paratrend intravascular combined PO2, PCO2, and pH sensor (hybrid electrochemical/optical design) (C) needle type electrochemical glucose sensor useful for monitoring glucose subcutaneously to track blood glucose levels continuously.

Several implanted biosensors have been developed and evaluated in both animals and humans (see Chapter 4). Detection systems are based on enzymes, electrodes, or fluorescence. The most widely studied method is an electrochemical sensor that uses glucose oxidase. This sensor can be implanted intravenously or subcutaneously. Intravenous implantation in dogs for up to 3 months has demonstrated the feasibility of this approach. Alternatives to enzymes are being developed, including artificial glucose receptors. Less success has been achieved with subcutaneous implants. Implantation of a needle type of sensor into the subcutaneous tissue induces a host of inflammatory responses that alters the sensitivity of the device. Microdialysis with hoUow fibers or ultrafiltration with biologically inert material can decrease this problem. 

The studies by Shichiri s group led to an artificial pancreas consisting of a needle-type glucose sensor, a computer, and two syringe-driving systems, with a total weight of 400 g. Yet years will have to pass until a robust and reliable equipment for everyday use will be available. 

Needle-type glucose sensors may be advantageously introduced into interstitial fluid [389, 394,395]. As shown in animal experiments, in this manner a measuring range of 3.3-27.7 mM can be obtained [395]. Combination of a cellulose diacetate membrane containing GOD with a hydrophilic alginate-polylysine-alginate membrane provides a response time of 5 min and a stability of 7 d [389]. The increased lifetime of the sandwich membrane is due to better biocompatibility. 

A needle-type glucose sensor covered by a biocompatible membrane has been described recently [47]. However, no in vivo results are reported. 

Shichiri M, Kawamori R, Yamasaki T et al. Wearable-type artificial pancreas with needle-type glucose sensor. Lancet 1982 ii l 129-1131. 

Device structures adopted for resistor type sensors in practice, (a) Sintered block, (b) thin alumina tube-coated layer, (c) screen printed thick film, (d) small bead inserted with coil and needle electrodes, (e) small bead inserted with a single coil (heater and electrode), (f) practical sensor element assembling sensor device, metal cap and filter. 

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