SubscribeThe next generation of biosensor to reach the market has to achieve considerable advancements over the current standard.
Sensors must be capable of providing a mature technological base that is capable of large improvements in performance and practicality, with the major market forces being:
- Reduction of false alarms (both positive and negative)
- Increased discrimination
- Improved reliability and reduced sensor down-time
- Reduced device cost, weight and size
One method currently being considered / employed is to design out the need for large, complicated and expensive bulk solid state lasers with the use of new semiconductor lasers. Given the advancements currently underway in the field of semiconductor lasers and with the benefits including reduced costs, size and complexity it appears that these devices would be a useful alternative to the conventional solid state laser.
However, despite the current high level of anticipation these sources are limited in their wavelength capabilities and are only capable of producing wavelengths around 400 nm in a reliable and cost effective package suitable to this type of application. Given the current state of development it is likely that a source in the desired 266-300 nm emission wavelength band would be capable of integration into bio-sensors sometime within the next 5 years.
The strategy at BIRAL is to introduce a family of real-time bio-detection sensors with a number of technical innovations enhancing performance and practicality. No single instrument will fit all biodetection applications and it is our belief that a range of optical sensors giving a variety of performance versus cost options is the best way to address the needs of networks of low cost sensors along with those of point detection triggers.
Biral's response to the aforementioned market forces has been to increase the number of measured independent particle parameters giving more information to reject irrelevant background particles from the data and reducing the probability of false alarms. The result is a bio-sensor that is capable of detecting four independent particle characteristics; size, shape, fluorescence and particle count - see Figure 4.
Figure 4. Representation of the reduction in false alarms through the use of multiple particle characteristics.
The false alarm rate of a sensor can be reduced by increasing the number of independent aerosol characteristics. The specific advantage of the introduction of the fluorescence characterisation is that the false alarms that would occur between the size-shape, or the size-fluorescence information are significantly reduced.
The intention behind this strategy is remove as many of the false alarms as possible and only leave those alarms that actually look like potential bio-agents. It can not be assumed that a previously unseen (or uncharacterised) bio-agent is not present and so the systems should not be over-designed in such a way that these agents are missed. This can be achieved by the cross-correlation of as much information as possible: i.e. size, shape, fluorescence and count characterisation.
To the best of our knowledge no other optical biosensor is capable of real-time determination on as many particle discriminators. For this new development we have retained the advantages of 280 nm excitation of tryptophan by the introduction of a novel light source. This new source is an innovative introduction to the bio-sensor detection capability of the instrument and will provide a low cost alternative to the conventional solid state laser source.
Furthermore, the new device has a lifetime of years, requires no maintenance, is reliable and also of importance is that the optical performance degradation is negligible over the lifetime of the device.
Figure 4. Representation of the reduction in false alarms through the use of multiple particle characteristics.
The false alarm rate of a sensor can be reduced by increasing the number of independent aerosol characteristics. The specific advantage of the introduction of the fluorescence characterisation is that the false alarms that would occur between the size-shape, or the size-fluorescence information are significantly reduced.
The intention behind this strategy is remove as many of the false alarms as possible and only leave those alarms that actually look like potential bio-agents. It can not be assumed that a previously unseen (or uncharacterised) bio-agent is not present and so the systems should not be over-designed in such a way that these agents are missed. This can be achieved by the cross-correlation of as much information as possible: i.e. size, shape, fluorescence and count characterisation.
It is the symbiosis of these two detector strategies (UK and US) and the experience BIRAL has gained with the UK's ASAS™ technology that makes us believe that the addition of fluorescence measurements will lead to a large step forward in the field of biological aerosol detection.
The new detector called VeroTect™, has been and is currently involved in a series of in-house and external trials, including tests with bacterial and viral agent simulants. In addition to these tests, the device has also been characterised for common interferants.
The device has shown very good trials performance and the combination of the ASAS™ size and shape characterisation with the fluorescence detection has proved to be capable of the detection of bio-agent simulants. It is not our intention to provide a detail performance for the VeroTect™ bio-sensor in this paper, however a brief summary of the expected performance based on the current design is described.
VeroTect bio-sensor
As described above the new bio-sensor manufactured by BIRAL envelops the detection strategies of size, shape, fluorescence and particle count. The device is a complete USB interfaced detector that is designed with remote operation and surveillance in mind.
The device can be operated via battery power, has a low power consumption and a near zero logistics burden. As with the ASAS™ devices on the market today, the detectors are factory calibrated and the size and shape detector channels are not adjustable. However, in order to increase the usability of the device the fluorescence detection system is user programmable. The fluorescence detection works on the bulk media principle and is supplied by the same sample airflow used to measure the size and shape profile of the aerosol sample - see Figure 5.
In this way the fluorescence and size-shape information can be directly related. Furthermore, the rate at which the bulk fluorescence information is calculated can be adjusted to increase the time resolution of the instrument - a function that will produce more temporally accurate information in times of heightened risk of bio-activity.
In addition to this functionality it is proposed that the instrument can be used in a manner that will allow automatic gain control of the fluorescence measurements so that when there is very high biological activity the device will provide a reduced sensitivity.
This would ensure that the information gained has a large dynamic range, but is still capable of the required resolution. By using such an automatic gain control it is envisaged that the device will be capable of producing fluorescence information in even the most challenging situations and as a consequence would exhibit no loss of detection capability due to the presence of large amounts of fluorescent interferants.
Figure 5. Measured bulk fluorescence on an aerosol sample by the VeroTect™ instrument.
The data displayed shows the particle count recorded (×10), the Ultra-violet (UV) power monitor and the measured response of two fluorescence channels. Fluorescence Channel 1 shows the response in the near UV and Fluorescence Channel 2 the response in the near UV to Visible.
The relative responses of the fluorescence channels can be used to describe the fluorescence properties of the bulk aerosol and it is clear for this sample that the UV response is significantly larger than the response of the visible channel shown. In this example the sampling rate was 2 Hz, although this is user variable. Note the data points shown are for illustrative purposes only and different fixed off-sets have been applied to the data sets to aid in the presentation of the graph.
The sensor has a detection capabilty that exceeds that of the existing ASAS™ systems. While the underlying operating principles are the same for the size-shape information for both instruments, the VeroTect™ instrument has additional software functionality that allows for greater processing control of the data.
Both systems are capable of detecting size particles in the detection range of 0.5 - 15 microns in diameter and shaped particles are represented in asymmetry factor or aspect ratio format, with values ranging from 0-100 (0 being perfectly spherical). The VeroTect™ software allows for the adjustment of the size-shape information displayed to the user and as a consequence the user can concentrate on the area that is of most interest*1.
This ability allows for an individual instrument to be calibrated for a preferred detection range (likely detection ranges are 0.5-10, 0.5-15 or 0.5-20 microns diameter, although other ranges could be offered as custom designs). Furthermore additional graphical displays have been incorporated that allow for greater ease of use and are simpler to understand by the user.
The operational ability to detect fluorescent bio-particles has been assessed by the use of simulants (both biological and non-biological) and the device is expected to be capable of a resolution down to counts of viable bio-agent particles of approximately 10ℓ-1 as measured in the local aerosol environment.
In principle the bio-detection capability is limited to the fact that the actual aerosol distribution measured is dependant on statistical variations and only measurements on the level of single particles or greater can be detected. This resolution uses the 'laboratory' based determination of aerosol concentration for discretely generated aerosol samples (both biological and non-biological in nature) and an instrument with a concentrator to increase the sampled particular count. The concentrator used in this calculation was ´10 over the size range of particles sampled and the concentrator was taken to be 100% efficient*2.
As well as the ASAS™ functionality described above the new sensor has a suite of discrimination algorithms which use the comparative analysis of data to information stored in a library, such as common interferants (e.g. fuel oils). The library can be updated and new aerosol information introduced, either by BIRAL or the user, to enhance the identification capabilities of the device.
For the purpose of security the library is stored on the control computer and not onboard the instrument. This security feature serves two main purposes. Firstly the instrument can be positioned in sensitive areas where the risk of tampering is large without the risk of sensitive information, for example discrimination algorithms or bio-agent properties, falling into the possession of unauthorised personnel. Secondly the library can be updated remotely and access to the library is available to new sensors added to a network without the need of modification to existing or new sensors.
Such functionality leads to a much increased sensor capability and as a consequence a far wider range of applications for the user. Additional functionality is also likely to be available with the device, with possible modular additions including the use of Global Positioning (GPS) sensors, meteorological sensors and other COTS devices. BIRAL is already a manufacturer of meteorological sensors and produce ruggedised, fully weather proof and reliable sensors in the well known HSS sensor range.
It is anticipated that the device will find markets in applications where bio-agent detection is required due to concerns to health. Furthermore, the device need not be used only in military and civilian bio-detection projects, as the technology also lends itself to general national defence applications, particular monitoring and situations where it is required to measure the level of bacterial activity in the environment, whether locally or in a wider arena.
Further applications are in the field of general particle monitoring, including the sensing and description of combustion products, leading to the ability to detect personnel and vehicle movements remotely and automatically.
The intention behind this strategy is remove as many of the false alarms as possible and only leave those alarms that actually look like potential bio-agents. It can not be assumed that a previously unseen (or uncharacterised) bio-agent is not present and so the systems should not be over-designed in such a way that these agents are missed. This can be achieved by the cross-correlation of as much information as possible: i.e. size, shape, fluorescence and count characterisation.
It is the symbiosis of these two detector strategies (UK and US) and the experience BIRAL has gained with the UK's ASAS™ technology that makes us believe that the addition of fluorescence measurements will lead to a large step forward in the field of biological aerosol detection.
The new detector called VeroTect™, has been and is currently involved in a series of in-house and external trials, including tests with bacterial and viral agent simulants. In addition to these tests, the device has also been characterised for common interferants.
The device has shown very good trials performance and the combination of the ASAS™ size and shape characterisation with the fluorescence detection has proved to be capable of the detection of bio-agent simulants. It is not our intention to provide a detail performance for the VeroTect™ bio-sensor in this paper, however a brief summary of the expected performance based on the current design is described.
VeroTect bio-sensor
As described above the new bio-sensor manufactured by BIRAL envelops the detection strategies of size, shape, fluorescence and particle count. The device is a complete USB interfaced detector that is designed with remote operation and surveillance in mind. The device can be operated via battery power, has a low power consumption and a near zero logistics burden. As with the ASAS™ devices on the market today, the detectors are factory calibrated and the size and shape detector channels are not adjustable.
However, in order to increase the usability of the device the fluorescence detection system is user programmable. The fluorescence detection works on the bulk media principle and is supplied by the same sample airflow used to measure the size and shape profile of the aerosol sample - see Figure 5.
Figure 5. Measured bulk fluorescence on an aerosol sample by the VeroTect™ instrument.
The data displayed shows the particle count recorded (×10), the Ultra-violet (UV) power monitor and the measured response of two fluorescence channels. Fluorescence Channel 1 shows the response in the near UV and Fluorescence Channel 2 the response in the near UV to Visible.
The relative responses of the fluorescence channels can be used to describe the fluorescence properties of the bulk aerosol and it is clear for this sample that the UV response is significantly larger than the response of the visible channel shown. In this example the sampling rate was 2 Hz, although this is user variable. Note the data points shown are for illustrative purposes only and different fixed off-sets have been applied to the data sets to aid in the presentation of the graph.
In this way the fluorescence and size-shape information can be directly related. Furthermore, the rate at which the bulk fluorescence information is calculated can be adjusted to increase the time resolution of the instrument - a function that will produce more temporally accurate information in times of heightened risk of bio-activity. In addition to this functionality it is proposed that the instrument can be used in a manner that will allow automatic gain control of the fluorescence measurements so that when there is very high biological activity the device will provide a reduced sensitivity.
This would ensure that the information gained has a large dynamic range, but is still capable of the required resolution. By using such an automatic gain control it is envisaged that the device will be capable of producing fluorescence information in even the most challenging situations and as a consequence would exhibit no loss of detection capability due to the presence of large amounts of fluorescent interferants.
