New Worlds" Haifa researchers carry out sensitive detection of DNA sequences

The technique enables detection of DNA sequences at a sensitivity more than 1,000 times higher than that of existing methods.

By
February 7, 2016 02:14
Lab

Lab technician using microscope. (photo credit: INGIMAGE / ASAP)

 
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Researchers at the Technion-Israel Institute of Technology in Haifa have developed an innovative method for detecting DNA sequences with high sensitivity and published their study, highlighted on the cover of the journal Advanced Functional Materials.

The technique enables detection of DNA sequences at a sensitivity more than 1,000 times higher than that of existing methods, they said, adding that the principles of the study could enable the development of a wide range of simple and relatively inexpensive medical diagnostic systems. For example, they could identify known DNA mutations.

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The research was a multidisciplinary collaborative effort of the research groups of associate Prof. Ester Segal (of the faculty of biotechnology and food engineering) and assistant Prof. Moran Bercovici (faculty of mechanical engineering).

Doctoral student Rita Vilensky, who conducted the study under their guidance, built a lab-on-a-chip device combining a biosensor for optical detection of DNA molecules; and a system of microchannels enabling the concentration of DNA by applying electric currents on the chip.

Segal’s lab is developing optical biosensors based on silicon chips with nano-scale pores. The resulting perforated chip has a typical optical characteristic in the visible spectrum,” she explained.

“We bind to it one of the complementary strands comprising the DNA molecule that we want to identify. When we expose the chip to many sequences we can specifically identify the recognition reaction between the complementary DNA sequences.”

Specific capture of DNA molecules within the silicon nanostructure “causes a change in the spectrum of light reflected from the chip and enables us to easily identify and quantify these molecules, thereby ‘catching’ the sequence and knowing how much of it we have,” she noted.



One of the main limitations of this process is the sensitivity of the sensors, which is sometimes insufficient, especially for medical diagnostics applications.

At this point, Bercovici – who is developing microfluidic- based methods for increasing concentrations of biological molecules – joined the study.

“By using the appropriate chemistry and applying electric fields, we can concentrate the DNA molecules in tiny volumes and transport them to the sensor,” explained Bercovici.

“This way we ‘‘trick’ the sensor, presenting it with DNA concentrations that are 10,000 times higher than the natural concentrations in the sample.”

Through precise design of the silicon’s structure and controlled growth of insulating oxide layers, the researchers were able to apply high electric voltages on the chip while preserving its unique nanostructure.

“Combining the technologies has enabled us to improve the sensor’s sensitivity by a factor of between 1,000 and 10,000 compared with existing devices.”

PUTTING A SHINE ON DISAPPOINTING PRIZES Putting in a lot of effort to earn a reward can make unappealing prizes more attractive to kindergarteners, but not to preschoolers, according to research published in Psychological Science, a journal of the Association for Psychological Science.

The findings revealed that when six year olds worked hard to earn stickers that they ultimately didn’t like, they were unwilling to give them up, but four year olds were quite eager to give the unappealing stickers away.

“When effort leads to an unsatisfying reward, adults experience a cognitive dissonance, arguably resolved by re-appraising the reward’s value,” explained Bar-Ilan University psychological scientist Avi Benozio, a lead researcher on the study.

“We found this dissonance to occur already among four and six year olds. Whereas six year olds reduced the dissonance by keeping their reward and boosting its value afterwards, four year olds took quite a different approach and detached themselves from the source of the discomfort by getting rid of the unsatisfying rewards.”

Benozio and co-author Gil Diesendruck recruited 45 preschool- aged (roughly four years old) and 53 kindergarten- aged (about six years old) children to participate in the study. They were told that they would be able to earn stickers by completing various tasks. Children who were randomly assigned to a high-effort group earned stickers by performing tasks that included counting as high as they could and reciting as much of the alphabet as they could. Children in the low-effort group earned stickers by answering basic questions, such as “How old are you?” and “What is the name of your teacher?” All of the children ultimately earned 10 stickers. They were then told they would be playing a “stickers game” in which they had to decide how many stickers they wanted to give to a child they had seen in a video. The researcher explained that they could choose to give as many or as few stickers as they wanted.

Critically, some of the participants earned stickers that were rated as attractive and highly valued by an independent group of children (such as Dragon Ball and SpongeBob stickers for 6-year-old boys); other participants earned stickers that were unattractive and of low value (such as Disney princess and plant stickers for 6-year-old boys).

The results showed that, overall, both the four year olds and the six year olds chose to give away fewer attractive stickers than unattractive stickers. But when the researchers examined the data further, they found that effort mattered a lot to six year olds. With attractive stickers, the children gave away about 21 percent if they had been relatively easy to get but only about 10% when they were hard-earned. Similarly, they gave away 30% of the unattractive stickers that were easily acquired, but only 17% of the unattractive stickers that were hard to get.

Intriguingly, effort didn’t seem to influence four year olds’ decision making. When the stickers were attractive, they gave away roughly the same percentage, regardless of how hard they had worked to earn them. And the four year olds actually gave away significantly more unattractive stickers when they had been hard to get, compared to when they were easily earned.

The researchers suggest that six year olds, just like adults, tend to employ a cognitive strategy to accommodate the knowledge that they worked hard to earn an unattractive reward. Specifically, they translated their effort into value, choosing to keep more of the unappealing, hard-to-get stickers for themselves.

The younger children, however, seemed to make use of a behavioral strategy that involved distancing themselves from the offending stickers, choosing simply to part with more of them.

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