Photon-Counting Means Sensitivity
 

The two main types of detection used with photomultipliers are photon-counting and analog.

Photon-Counting Mode
When photons of light strike the cathode of a photomultiplier tube (PMT), they dislodge elec­trons. These electrons pass from the cathode into the dynode chain (a series of high-voltage steps), which amplifies and directs them, to the anode.
The pulses are then transmitted to an amplifier, and then on to a discriminator, which filters out the lower-intensity noise pulses. A second amplifier  changes the volt­age to a useable level.

The advantages of photon-counting are:

The signal-to-noise ratio of the data is higher. Most noise is generated after the cathode, usu­ally in the dynode chain. These noise pulses are lower intensity and are removed by the dis­criminator. In the analog system, noise gets added directly to the signal, and thus cannot be removed.
The stability of a photon-counting system is better. All PMTs need a high-voltage supply. A small change in the voltage supplied will not af­fect the pulse count of a photon-counting sys­tem; bill will affect the analog portion because of the integration of pulse height changes.
Photon counting is unaffected by an RC time constant, which is an inherent part of analog systems’ electronics. (The RC time-constant re­fers to an electronic circuit made of a resistor and capacitor.) Analog systems rely on RC time-constants to reduce noise, but thereby ex­tract a price. One problem introduced by the RC time-constant is accuracy. An RC circuit discharges only 67% of its charge after one time constant has elapsed. For example, with a time constant of one second, 33% of the signal still is stored within the circuit, reducing the ac­curacy. Another problem is the speed of the electronics. At any signal level, RC circuits ap­proach their final value exponentially; thus, the faster you scan, the more skewed your data look. This effect does not happen to digital sig­nals, such as with photon counting.
The precision, or practical range, of photon counting is greater than most analog systems. The range for photon counting is usually based on the PMT or the band pass of the first ampli­fier, in the range of 3–4 million counts per sec­ond. Analog systems are usually based on the range of the analog-to-digital converter (ADC).
on the other hand, the range is 0 to 3 million. This means that small changes and signals will be more clearly resolved via photon counting.
Analog Mode
In analog mode, electrons also are generated by photons of light striking the cathode of a PMT. The resulting analog signal from the anode is the DC portion of the pulses. Bear in mind that this DC cur­rent is the sum of all pulses regardless of their source (cathode, dynode chain, leaky components, etc.). Therefore, the noise is more tightly bound to
Photon-Counting vs. Analog
With strong light intensity, such as in absorp­tion measurements, analog methods may be ade­quate. For low-light techniques, such as fluores­cence or spectroscopes, photon-counting enables you to extract the maximum information from your data.

 

Chemiluminescence.

Chemiluminescence is the light emission accompanying some chemical reactions. Chemiluminescence accompanies energetic redox reactions, e. g. interaction of two radicals or reactions where peroxides are involved. Intrinsic (ultraweak) chemiluminescence of human and animal cells and tissues is the result of reactions of free radicals, including nitric oxide and radicals of oxygen and lipids

 

Cell  Chemiluminescence.


The Cell Chemiluminescence method allows revealing presence of inflammation focuses.  With acute heart pain state (cardiodynia) the Chemiluminescence method  allows differentiating myocardial ischemia from myocardial infarction, as in the case of infarction the cell chemiluminescence intensity increases 100 times as much. The Chemiluminescence method allows detecting myocardial infarction focuses in the cases when they are not observed by electrocardiographical examination – for example, with posterior mycrocardial infarction.

The Chemiluminescence method allows estimating the level of disease gravity and efficiency of the therapy performed in most cases of inflammatory diseases, including rheumatoid arthritis, lung diseases (pulmonary tuberculosis, acute pneumonia), and in inflammation focuses of internal organs (destructive appendicitis, pancreatitis, cholecystitis).

Preventive medicine


Chemiluminescence of blood serum shows the level of antioxidant reserves of the organism as its lowering points out at the risk factor of stimulation of various kinds of diseases. The method allows checking-up antioxidant therapy (vitamins C and E) and medical preparation treatment efficiency.

Determination of blood serum chemiluminescence intensity allows estimating the oxidized lipoprotein rate in blood, as the heightened concentration of oxidized lipoproteins is the essential index of the risk factor of atherosclerosis and essential hypertention challenge.

LIGHT EMISSION ACCOMPANYING BIOCHEMICAL REACTIONS
Yu. A. VLADIMIROV

ENHANCED CHEMILUMINESCENCE AND BIOLUMINESCENCE AS AN ANALYTICAL TOOL IN BIOMEDICAL INVESTIGATIONS
Yu. A. VLADIMIROV

 

Универсальный хемилюминометр SmartLum 5773

История создания
2004 – 2009
г. Москва


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