Low-Noise PCR Cyclers for an Optimized Lab

Sustained noise exposure has a negative impact on people’s health, ability to concentrate and performance. A major part of the noise level in a lab is emitted by different types of equipment like smaller centrifuges, various power supplies and thermal cyclers. This application note evaluates the noise level generation of six thermal cyclers in 3 operational states. The obtained values reveal that the new Eppendorf Mastercycler® X40 stands out among its competitors both in terms of emitted noise levels and potential annoyance by tonality. Introduction The development of work processes in modern laboratories has led to an increased usage of electronic equipment emitting noise. The diverse negative effects of noise pollution on humans have been investigated in numerous scientific articles [1-4]. The WHO Environmental Noise Guidelines for the European Region delivers substantial evidence that connects environmental noise exposure to adverse health outcomes [5]. Hence, noise levels should be considered when comparing standard lab equipment such as thermal cyclers within the same market range. This application note evaluates both the absolute noise levels and an additional factor, the tonality, which can contribute to a perceived annoyance, of six thermal cyclers. A noise is tonal if it contains a recognizable tone for the human ear, that stand out from the average background noise [6]. The presence of such tone is perceived as annoying by most people [7]. All six devices were measured by the independent technical inspection association TÜV NORD under 3 different operational states.APPLICATION NOTE I No. 474 I Page 2 Manufacturer Model Eppendorf Mastercycler® X40 Bio-Rad® T100TM VWRTM XT96 Himedia® Prima-96TM Applied Biosystems® SimpliAmpTM Bioneer AllinOneCyclerTM Table 1: List of thermal cyclers under examination The sound power level was determined by TÜV NORD in A-weighted decibel [dB(A)] for six thermal cyclers listed in Table 1 in accordance with DIN EN ISO 3744. Material and Methods The measurements were taken at the following three operational states: 1. Idle state: Thermal cycler switched on, temperature control of block and lid turned off, with no application running on device. 2. Continuous (hold step) temperature control of the block at 4 °C. 3. Standard 3-step PCR program shown in Table 2. Lid 105 °C Eppendorf Header Settings Energy-saving mode Temperature mode ON Standard 3-step PCR program Denaturation 95 °C/15 s Annealing 60 °C/15 s Elongation 72 °C/30 s Table 2: Settings of the used Standard 3-step PCR program All measurements were performed using an inserted 96 well PCR plate (high profile unskirted Eppendorf twin.tec® PCR Plate 96). The plate positions of columns 1, 3, 5, 8, 10, 12 were filled with 30 μL H₂O each, thus filling 48 of the 96 well positions. The plate was sealed with Eppendorf Heat Sealing Foil using the HeatSealer 200 from Eppendorf to prevent evaporation. APPLICATION NOTE I No. 474 I Page 3 Result and Discussion The six tested cyclers emitted different sound power levels in the three tested operational states (idle, PCR run and 4 °C). In particular, the average noise level of the Mastercycler X40 and Prima-96TM during idle state (Figure 1) were 30.2 and 30.1 dB(A), respectively. These values are too low for relevant differentiation of the operating noise to the surrounding sound level. However, thermal cyclers T100TM and AllinOneCyclerTM emitted a comparable high sound power level of 54.2 and 57.7 dB(A) in the idle state, respectively. In human sound perception, an increase of sound power level by 10 dB(A) means a doubling of the loudness [8, 9]. Hence, the generated noise in the idle state of both cyclers is perceived more than 4 times stronger than noise emitted by the Mastercycler X40, and Prima-96. Figure 1: Sound power levels of the thermal cyclers during three operational states. Measurements with tonality indicated with purple lines. 25 30 35 40 45 50 55 60 65 Mastercycler® X40 T100TM XT96 Prima-96TM SimpliAmpTM AllinOneCyclerTM Sound power level [db (A)] Idle PCR run 4°C 30.2 40.5 54.2 54.9 40.9 55.3 36.6 39.3 53.5 30.1 56.5 57.1 44.0 56.1 55.9 57.7 59.4 59.6 Sound power level [dB(A)] XT96 Prima-96TM SimpliAmpTM AllinOneCyclerTM PCR Run Mastercycler® X40 T100TM 25 30 35 40 45 50 55 60 65 Mastercycler® X40 T100TM XT96 Prima-96TM SimpliAmpTM AllinOneCyclerTM Sound power level [db (A)] Idle PCR run 4°C PCR Run Idle 4 °CAPPLICATION NOTE I No. 474 I Page 4 During a standard 3-step PCR program (table 2) the cycler XT96 and Mastercycler X40 generated comparable low sound power levels of 39.3 and 40.5 dB(A), respectively. As the following passages will pay attention to sound power levels and sound pressure level, the difference of both terms is explained shortly. The “sound power level is the acoustic energy emitted by a source which produces a sound pressure level at some distance. While the sound power level of a source is fixed, the sound pressure level depends upon the distance from the source and the acoustic characteristics of the area in which it is located” [10]. According to the recommendation of ISO 11690-1[11] the sound pressure should not exceed 45 dB(A) for meeting rooms or tasks involving concentration. Since the here presented sound power levels were determined in an essentially free sound field above a reflecting plane, a correction factor of 8 dB(A) was subtracted (as recommended by the TÜV) to obtain the sound pressure level in a 1 m distance. A sound source will produce a higher sound pressure level in a small reflective room than in a large acoustically dead room [10]. The sound power levels of the cycler T100, Prima-96, SimpliAmpTM and AllinOneCycler ranged between 54.9 and 59.4 dB(A). Thus, these values represent corrected sound pressure levels between 46.9 and 51.4 dB(A) which are not recommended for tasks involving concentration. Similarly, these four cyclers reached noise pressure values over 45 dB(A) during continuous temperature control of the block at 4 °C. The intensity of the operational noise power level under different states for each thermal cycler varied within the range of approximately 1 (T100) and 27 dB(A) (Prima-96). Hereby, the biggest span is detected between cyclers that have very low noise when idle to being loudest when cooling at 4 °C, such as shown by thermal cyclers XT96 and Prima-96 (Figure 1). During all operational states the Mastercycler X40 did not exceed a sound power level of 41 dB(A). All other cyclers exceeded a sound power level of 55 dB(A) in at least one of the operational states. The AllinOneCycler generated the highest noise emission of 59.6 dB(A) during all three operational states. Even if the here detected noise power levels do not lead to hearing hazard they can cause stress and can be perceived 0 5 10 15 20 25 30 35 40 45 50 16 31.5 63 125 250 500 1k 2 k 4 k 8 k Idle PCR-Run 4°C Medium surface sound pressure level [dB(A)] Frequenz [Hz] Tonality Idle PCR Run 4 °C Figure 2: Exemplary medium surface sound pressure level in a 1 m distance in dB(A) from thermal cycler XT96. A tonality detected at 315 Hz during a continuous hold step at 4 °C is indicated with a purple arrow.APPLICATION NOTE I No. 474 I Page 5 as annoying. To evaluate potential additional annoyance generated by cyclers even during activities below a hearing hazard-causing noise level, the presence of tonality was tested according to Norm DIN 45645-2 2012-09[12]. A sound is tonal when sound components are clearly audible and their presence by a third-octave analysis can be demonstrated [6] (see an example for tonality in Figure 2). Consequently, cycler SimpliAmp and AllinOneCycler are tonal during all operational states (purple lines in Figure 1). Furthermore, tonality was detected for cycler Prima-96 (PCR, 4 °C) and cycler XT96 (4 °C). The Mastercycler X40 as well as the T100 showed no tonality. It must be noted that the above data reflects the noise levels from a single thermal cycler. In a lab where there is usually more than one cycler at different operational states, the cumulative noise generation would be significant. Figure 3 shows the number of Mastercycler X40 devices which are theoretically needed to generate a comparable noise level as the other evaluated cyclers. Since cycler XT96 showed a similar sound power level than the Mastercycler X40 during the PCR run, one Mastercycler X40 device is needed to emit a comparable sound power level. 28, 40 and 36 Mastercycler X40 would have to be used simultaneously to emit a comparable noise level as the cycler T100, Prima-96 and SimpliAmp, respectively. As an extreme example, 78 Mastercycler X40 would be needed to reach the sound power level of one AllinOneCycler. Figure 3: Number (rounded to 1) of the Mastercycler X40 devices needed to generate a corresponding sound power level of the other tested cycler during a PCR program. 10 cyclers correspond to a doubling of the sound power level due to the logarithmic relationship of both parameters. During all operational states the measurement results presented here show that the Mastercycler X40 did not exceed a sound power level of 41 dB(A). Furthermore, no potential annoyance by tonality was detected for the Mastercycler X40 and the T